feat(GCS): Update `CustomTime` metadata field at cache entry hits #4256

Job	Run time
clippy ubuntu-latest	1m 4s
coverage ubuntu-22.04 rust nightly	6m 15s
clippy macOS-latest	1m 2s
build sccache x86_64-unknown-linux-musl	6m 1s
clippy windows-latest	2m 23s
coverage macos-13 rust nightly	5m 16s
check_features (azure)	46s
build sccache-dist x86_64-unknown-linux-musl	4m 26s
rustfmt ubuntu-latest	12s
check_features (gcs)	45s
build sccache aarch64-unknown-linux-musl	6m 15s
check_features (gha)	39s
build sccache armv7-unknown-linux-musleabi	6m 3s
check_features (memcached)	34s
build sccache i686-unknown-linux-musl	6m 8s
test freebsd-14.1 rust stable (ubuntu-22.04)	5m 27s
check_features (redis)	43s
test ubuntu-20.04 rust 1.75.0 cuda11.1	5m 46s
build sccache x86_64-apple-darwin	10m 24s
check_features (s3)	43s
test ubuntu-22.04 rust 1.75.0 dist-server	1m 49s
build sccache aarch64-apple-darwin	4m 56s
toml_format	8s
check_features (webdav)	42s
test ubuntu-20.04 rust stable	1m 49s
build sccache x86_64-pc-windows-msvc	14m 14s
test ubuntu-20.04 rust beta	2m 6s
build sccache aarch64-pc-windows-msvc	14m 29s
test ubuntu-20.04 rust nightly	1m 43s
test ubuntu-20.04 rust stable no-default-features	1m 6s
test ubuntu-22.04 rust stable cuda11.8	6m 8s
test ubuntu-24.04 rust 1.75.0 cuda12.8	4m 0s
test macos-13 rust stable	2m 45s
test macos-14 rust stable	1m 46s
test windows-2019 rust 1.75.0 cuda11.1	6m 2s
test windows-2019 rust nightly cuda11.8	5m 28s
test windows-2019 rust beta cuda11.8	5m 31s
test windows-2022 rust 1.75.0 cuda12.8	5m 42s
test windows-2022 rust nightly cuda12.8	5m 3s
test windows-2022 rust beta cuda12.8	5m 18s
release	0s
	2h 41m 37s

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