Add C `Contracts` package #2676

Job	Run time
Prepare CodeQL unit test matrix	3s
Run unit tests (cpp, 2.14.6, codeql-cli/v2.14.6, codeql-bundle-v2.14.6, ubuntu-latest-xl, codeql-...	32m 33s
Run unit tests (c, 2.14.6, codeql-cli/v2.14.6, codeql-bundle-v2.14.6, ubuntu-latest-xl, codeql-cl...	17m 39s
Validate test results	3s
	50m 18s

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