Expose `MetadataCommand::env` from `cargo_metadata` #1595

Job	Run time
Cross-compile to aarch64	2m 52s
Build documentation (ubuntu-latest)	55s
Build and test (all features) (ubuntu-latest, 1.78)	3m 56s
Build and test core crates (ubuntu-latest, 1.78)	2m 26s
Build and test (all features) (ubuntu-latest, stable)	2m 24s
Build and test core crates (ubuntu-latest, stable)	2m 14s
Lint	1m 58s
cargo-compare extended tests (ubuntu-latest)	5m 17s
Build and test (all features) (macos-14, 1.78)	2m 51s
Build and test core crates (macos-14, 1.78)	2m 8s
cargo-compare extended tests (macos-14)	1m 37s
Build and test (all features) (macos-14, stable)	3m 32s
Build and test core crates (macos-14, stable)	1m 24s
Build and test (all features) (windows-latest, 1.78)	7m 21s
Build and test core crates (windows-latest, 1.78)	4m 19s
Build and test (all features) (windows-latest, stable)	5m 7s
Build and test core crates (windows-latest, stable)	5m 19s
	55m 40s

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