Use only `FoundationEssentials` when possible #57

Job	Run time
Semantic Version label check	3s
Unit tests / Construct unit test matrix	2s
Swift 6 Language Mode / Swift 6 language mode	52s
Soundness / Broken symlinks check	3s
Soundness / API breakage check	1m 10s
Soundness / Documentation check	35s
Soundness / Format check	32s
Soundness / License headers check	2s
Soundness / Shell check	32s
Soundness / Unacceptable language check	2s
Soundness / Python lint check	4s
Soundness / YAML lint check	2s
Unit tests / Unit tests / Linux (6.0)	1m 0s
Unit tests / Unit tests / Linux (nightly-6.0)	1m 5s
Unit tests / Unit tests / Linux (nightly-main)	1m 12s
	7m 16s

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