refactor: Move constructors to the top of `SteamDir`s impl #147

Job	Run time
validation (ubuntu-latest, stable)	19s
wasm	34s
validation (ubuntu-latest, beta)	26s
validation (macos-latest, stable)	24s
validation (macos-latest, beta)	25s
validation (windows-latest, stable)	1m 42s
validation (windows-latest, beta)	55s
	4m 45s

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