unified-scheduler can not be built using nightly rustc due to polyfill API mismatch

[alexpyattaev]

Problem

https://crates.io/crates/vec_extract_if_polyfill is outdated and no longer matches the API offered in nightly rust.
For reference the new API includes additional range argument https://doc.rust-lang.org/std/vec/struct.Vec.html#method.extract_if

This means that unified-scheduler can no longer be built using nightly rustc

agave/unified-scheduler-pool/src/lib.rs

Line 381 in 1bcf743

// Use the still-unstable Vec::extract_if() even on stable rust toolchain by

Proposed Solution

Maybe just copy the implementation from the library into our sources until feature stabilizes?

[ifiokjr]

I didn't see this before creating #5322.

I've also opened a pull request for it.