feat: Make `reason_phrase` a String #2652

Job	Run time
Build & test (ubuntu-latest, 1.74.0, debug)	12m 15s
Build & test (ubuntu-latest, stable, debug)	11m 34s
Build & test (ubuntu-latest, nightly, debug)	11m 49s
Build & test (macos-14, 1.74.0, debug)	11m 42s
Build & test (macos-14, stable, debug)	9m 16s
Build & test (macos-14, nightly, debug)	10m 2s
Build & test (windows-latest, 1.74.0, debug)	20m 41s
Build & test (windows-latest, stable, debug)	21m 22s
Build & test (windows-latest, nightly, debug)	21m 32s
Build & test (ubuntu-latest, stable, release)	17m 54s
Benchmark / Benchmark	24m 32s
	2h 52m 39s

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