Add support for Nim (with tests) #2954

Job	Run time
Output Regression Test	5m 37s
Test Linux (latest stable Rust)	1m 59s
Test with MIME database	4m 42s
Test x86_64-unknown-linux-gnu	4m 44s
Test x86_64-apple-darwin	6m 38s
Actionlint	1m 0s
Rustfmt	1m 23s
Test x86_64-pc-windows-msvc	6m 4s
Test aarch64-unknown-linux-gnu	5m 49s
Check Linux Packaging	4m 54s
Test x86_64-unknown-linux-musl	5m 2s
	47m 52s

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