fix the forwarding of the receiver in the just_from algorithm

[ericniebler]

Description

a typo in the just_from algorithm meant that a receiver is getting passed as an lvalue to a completion function. not all receivers have .set_[value|error|stopped]() members that are callable on lvalue object. this PR fixes the typo and correctly forwards the receiver.

as a drive-by, i also fix a conformance issue by making environments not move/copy assignable.

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[github-actions]

🟨 CI finished in 13m 35s: Pass: 96%/52 | Total: 2h 37m | Avg: 3m 01s | Max: 11m 50s | Hits: 68%/216

• 🟨 cudax: Pass: 96%/52 | Total: 2h 37m | Avg: 3m 01s | Max: 11m 50s | Hits: 68%/216

  🔍 cpu: amd64 🔍
    🔍 amd64              Pass:  95%/48  | Total:  2h 27m | Avg:  3m 03s | Max: 11m 50s | Hits:  68%/216   
    🟩 arm64              Pass: 100%/4   | Total: 10m 18s | Avg:  2m 34s | Max:  3m 35s
  🚨 cxx: Clang9 🚨
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    🟩 GCC9               Pass: 100%/2   | Total:  4m 47s | Avg:  2m 23s | Max:  2m 28s
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    🟩 GCC12              Pass: 100%/7   | Total: 21m 15s | Avg:  3m 02s | Max:  4m 02s
    🟩 GCC13              Pass: 100%/3   | Total:  8m 03s | Avg:  2m 41s | Max:  3m 35s
    🟩 MSVC14.36          Pass: 100%/1   | Total: 10m 34s | Avg: 10m 34s | Max: 10m 34s | Hits:  68%/108   
    🟩 MSVC14.39          Pass: 100%/1   | Total: 11m 50s | Avg: 11m 50s | Max: 11m 50s | Hits:  68%/108   
  🔍 cxx_family: Clang 🔍
    🔍 Clang              Pass:  93%/30  | Total:  1h 20m | Avg:  2m 41s | Max:  4m 15s
    🟩 GCC                Pass: 100%/20  | Total: 54m 09s | Avg:  2m 42s | Max:  4m 02s
    🟩 MSVC               Pass: 100%/2   | Total: 22m 24s | Avg: 11m 12s | Max: 11m 50s | Hits:  68%/216   
  🔍 jobs: Build 🔍
    🔍 Build              Pass:  95%/47  | Total:  2h 17m | Avg:  2m 55s | Max: 11m 50s | Hits:  68%/216   
    🟩 Test               Pass: 100%/5   | Total: 19m 36s | Avg:  3m 55s | Max:  4m 15s
  🔍 std: 17 🔍
    🔍 17                 Pass:  92%/28  | Total:  1h 13m | Avg:  2m 38s | Max:  3m 57s
    🟩 20                 Pass: 100%/24  | Total:  1h 23m | Avg:  3m 29s | Max: 11m 50s | Hits:  68%/216   
  🟨 cudacxx_family
    🟨 nvcc               Pass:  96%/52  | Total:  2h 37m | Avg:  3m 01s | Max: 11m 50s | Hits:  68%/216   
  🟨 gpu
    🟨 v100               Pass:  96%/52  | Total:  2h 37m | Avg:  3m 01s | Max: 11m 50s | Hits:  68%/216   
  🟨 ctk
    🟨 12.0               Pass:  94%/19  | Total: 57m 06s | Avg:  3m 00s | Max: 10m 34s | Hits:  68%/108   
    🟨 12.6               Pass:  96%/33  | Total:  1h 40m | Avg:  3m 02s | Max: 11m 50s | Hits:  68%/108   
  🟨 cudacxx
    🟨 nvcc12.0           Pass:  94%/19  | Total: 57m 06s | Avg:  3m 00s | Max: 10m 34s | Hits:  68%/108   
    🟨 nvcc12.6           Pass:  96%/33  | Total:  1h 40m | Avg:  3m 02s | Max: 11m 50s | Hits:  68%/108   
  🟩 sm
    🟩 90                 Pass: 100%/1   | Total:  2m 20s | Avg:  2m 20s | Max:  2m 20s
    🟩 90a                Pass: 100%/1   | Total:  2m 20s | Avg:  2m 20s | Max:  2m 20s
  

👃 Inspect Changes

Modifications in project?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
+/-	CUDA Experimental
	pycuda
	CCCL C Parallel Library

Modifications in project or dependencies?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
+/-	CUDA Experimental
	pycuda
	CCCL C Parallel Library

🏃‍ Runner counts (total jobs: 52)

#	Runner
41	linux-amd64-cpu16
5	linux-amd64-gpu-v100-latest-1
4	linux-arm64-cpu16
2	windows-amd64-cpu16

[github-actions]

🟩 CI finished in 14m 55s: Pass: 100%/52 | Total: 2h 39m | Avg: 3m 03s | Max: 11m 43s | Hits: 68%/216

• 🟩 cudax: Pass: 100%/52 | Total: 2h 39m | Avg: 3m 03s | Max: 11m 43s | Hits: 68%/216

  🟩 cpu
    🟩 amd64              Pass: 100%/48  | Total:  2h 29m | Avg:  3m 07s | Max: 11m 43s | Hits:  68%/216   
    🟩 arm64              Pass: 100%/4   | Total:  9m 30s | Avg:  2m 22s | Max:  2m 47s
  🟩 ctk
    🟩 12.0               Pass: 100%/19  | Total: 58m 18s | Avg:  3m 04s | Max: 11m 43s | Hits:  68%/108   
    🟩 12.6               Pass: 100%/33  | Total:  1h 41m | Avg:  3m 03s | Max: 10m 57s | Hits:  68%/108   
  🟩 cudacxx
    🟩 nvcc12.0           Pass: 100%/19  | Total: 58m 18s | Avg:  3m 04s | Max: 11m 43s | Hits:  68%/108   
    🟩 nvcc12.6           Pass: 100%/33  | Total:  1h 41m | Avg:  3m 03s | Max: 10m 57s | Hits:  68%/108   
  🟩 cudacxx_family
    🟩 nvcc               Pass: 100%/52  | Total:  2h 39m | Avg:  3m 03s | Max: 11m 43s | Hits:  68%/216   
  🟩 cxx
    🟩 Clang9             Pass: 100%/2   | Total:  5m 07s | Avg:  2m 33s | Max:  2m 39s
    🟩 Clang10            Pass: 100%/2   | Total:  5m 10s | Avg:  2m 35s | Max:  2m 43s
    🟩 Clang11            Pass: 100%/4   | Total: 10m 28s | Avg:  2m 37s | Max:  3m 05s
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    🟩 Clang14            Pass: 100%/4   | Total: 11m 58s | Avg:  2m 59s | Max:  3m 44s
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    🟩 Clang17            Pass: 100%/2   | Total:  5m 25s | Avg:  2m 42s | Max:  2m 46s
    🟩 Clang18            Pass: 100%/2   | Total:  8m 25s | Avg:  4m 12s | Max:  5m 35s
    🟩 GCC9               Pass: 100%/2   | Total:  4m 39s | Avg:  2m 19s | Max:  2m 22s
    🟩 GCC10              Pass: 100%/4   | Total:  9m 45s | Avg:  2m 26s | Max:  2m 30s
    🟩 GCC11              Pass: 100%/4   | Total: 10m 09s | Avg:  2m 32s | Max:  2m 37s
    🟩 GCC12              Pass: 100%/7   | Total: 23m 00s | Avg:  3m 17s | Max:  5m 22s
    🟩 GCC13              Pass: 100%/3   | Total:  7m 06s | Avg:  2m 22s | Max:  2m 47s
    🟩 MSVC14.36          Pass: 100%/1   | Total: 11m 43s | Avg: 11m 43s | Max: 11m 43s | Hits:  68%/108   
    🟩 MSVC14.39          Pass: 100%/1   | Total: 10m 57s | Avg: 10m 57s | Max: 10m 57s | Hits:  68%/108   
  🟩 cxx_family
    🟩 Clang              Pass: 100%/30  | Total:  1h 22m | Avg:  2m 44s | Max:  5m 35s
    🟩 GCC                Pass: 100%/20  | Total: 54m 39s | Avg:  2m 43s | Max:  5m 22s
    🟩 MSVC               Pass: 100%/2   | Total: 22m 40s | Avg: 11m 20s | Max: 11m 43s | Hits:  68%/216   
  🟩 gpu
    🟩 v100               Pass: 100%/52  | Total:  2h 39m | Avg:  3m 03s | Max: 11m 43s | Hits:  68%/216   
  🟩 jobs
    🟩 Build              Pass: 100%/47  | Total:  2h 17m | Avg:  2m 55s | Max: 11m 43s | Hits:  68%/216   
    🟩 Test               Pass: 100%/5   | Total: 22m 12s | Avg:  4m 26s | Max:  5m 35s
  🟩 sm
    🟩 90                 Pass: 100%/1   | Total:  2m 15s | Avg:  2m 15s | Max:  2m 15s
    🟩 90a                Pass: 100%/1   | Total:  2m 12s | Avg:  2m 12s | Max:  2m 12s
  🟩 std
    🟩 17                 Pass: 100%/28  | Total:  1h 13m | Avg:  2m 36s | Max:  4m 05s
    🟩 20                 Pass: 100%/24  | Total:  1h 26m | Avg:  3m 35s | Max: 11m 43s | Hits:  68%/216   
  

👃 Inspect Changes

Modifications in project?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
+/-	CUDA Experimental
	pycuda
	CCCL C Parallel Library

Modifications in project or dependencies?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
+/-	CUDA Experimental
	pycuda
	CCCL C Parallel Library

🏃‍ Runner counts (total jobs: 52)

#	Runner
41	linux-amd64-cpu16
5	linux-amd64-gpu-v100-latest-1
4	linux-arm64-cpu16
2	windows-amd64-cpu16