Remove `unreachable-code` feature #23385

Job	Run time
pre-commit	40s
Determine changes	10s
mkdocs	2m 20s
cargo fmt	19s
python package	1m 4s
cargo clippy	1m 39s
cargo test (linux)	5m 57s
cargo test (wasm)	1m 15s
cargo test (windows)	6m 11s
cargo fuzz	4m 9s
cargo udeps	1m 44s
formatter instabilities and black similarity	0s
test scripts	45s
benchmarks	6m 2s
test ruff-lsp	21s
ecosystem	8m 45s
	41m 21s

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