Add a 'compile-once-test' subcommand #45

Job	Run time
Benchmark	5m 31s
Test / Linux (nightly-main - jammy)	2m 48s
Test / Linux (6.1 - jammy)	2m 22s
Test / Linux (6.0 - jammy)	1m 8s
Test / Linux (6.2 - jammy)	2m 9s
Test / Linux (nightly-6.2 - jammy)	2m 21s
Test / Static Linux Swift SDK Build (${{ matrix.swift_version }} - ${{ matrix.os_version }})	0s
Soundness / API breakage check	1m 48s
Soundness / Broken symlinks check	6s
Soundness / Documentation check	1m 5s
Soundness / YAML lint check	6s
Soundness / Shell check	59s
Soundness / Python lint check	9s
Soundness / License headers check	6s
Soundness / Format check	0s
Test / Embedded Swift SDK for Wasm Build (${{ matrix.swift_version }} - ${{ matrix.os_version }})	0s
Test / macOS (Xcode ${{ matrix.xcode_version }} - ${{ matrix.os_version }} - ${{ matrix.arch }})	0s
Test / Windows (${{ matrix.swift_version }} - windows-2022)	0s
Soundness / Unacceptable language check	0s
Test / Swift SDK for Wasm Build (${{ matrix.swift_version }} - ${{ matrix.os_version }})	0s
	20m 38s

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