refactor: make Contract generic for Compiler and add metadata to Comp… #857

Job	Run time
clippy	50s
feature-checks	3m 41s
doctest	1m 22s
docs	1m 10s
fmt	16s
test stable (ubuntu-latest)	1m 17s
test stable --all-features (ubuntu-latest)	2m 9s
test 1.83 (ubuntu-latest)	1m 9s
test stable (macos-latest)	1m 32s
test stable --all-features (macos-latest)	2m 17s
test 1.83 (macos-latest)	1m 22s
test stable (windows-latest)	4m 47s
test stable --all-features (windows-latest)	6m 3s
test 1.83 (windows-latest)	4m 14s
	32m 9s

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