Use only `FoundationEssentials` when possible #52

Job	Run time
Semantic Version label check	3s
Unit tests / Construct unit test matrix	3s
Swift 6 Language Mode / Swift 6 language mode	56s
Soundness / Broken symlinks check	3s
Soundness / Documentation check	39s
Soundness / API breakage check	1m 8s
Soundness / Format check	29s
Soundness / License headers check	5s
Soundness / Unacceptable language check	5s
Soundness / Shell check	31s
Soundness / Python lint check	4s
Soundness / YAML lint check	3s
Unit tests / Unit tests / Linux (6.0)	57s
Unit tests / Unit tests / Linux (nightly-6.0)	1m 4s
Unit tests / Unit tests / Linux (nightly-main)	1m 6s
	7m 16s

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