Use only `FoundationEssentials` when possible #53

Job	Run time
Semantic Version label check	5s
Unit tests / Construct unit test matrix	3s
Soundness / Broken symlinks check	2s
Soundness / API breakage check	50s
Soundness / Documentation check	33s
Soundness / Format check	29s
Soundness / License headers check	3s
Soundness / Shell check	35s
Soundness / Unacceptable language check	3s
Soundness / Python lint check	5s
Soundness / YAML lint check	4s
Swift 6 Language Mode / Swift 6 language mode	56s
Unit tests / Unit tests / Linux (6.0)	51s
Unit tests / Unit tests / Linux (nightly-6.0)	59s
Unit tests / Unit tests / Linux (nightly-main)	1m 3s
	6m 41s

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