Make 'php-project feature an optional dependency #74

Job	Run time
build (ubuntu-latest, 26.3, false)	1m 1s
build (ubuntu-latest, 27.2, false)	50s
build (ubuntu-latest, 28.2, false)	51s
build (ubuntu-latest, 29.2, false)	56s
build (macos-latest, 26.3, false)	2m 56s
build (macos-latest, 27.2, false)	3m 20s
build (macos-latest, 28.2, false)	2m 27s
build (macos-latest, 29.2, false)	5m 44s
build (windows-latest, 26.3, false)	3m 17s
build (windows-latest, 27.2, false)	1m 49s
build (windows-latest, 28.2, false)	1m 25s
build (windows-latest, 29.2, false)	1m 36s
build (ubuntu-latest, snapshot, true)	50s
build (macos-latest, snapshot, true)	3m 6s
build (windows-latest, snapshot, true)	1m 39s
	31m 47s

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