Avoid allocation in `CowBytes` if possible #5690

Job	Run time
cargo-fmt	11s
cargo-fmt	11s
cargo-fmt	11s
cargo-fmt	11s
cargo-docs	7m 19s
cargo-docs	7m 19s
cargo-docs	7m 19s
cargo-docs	7m 19s
cargo-clippy (self-hosted, ubuntu-20.04-x86-64)	9m 4s
cargo-clippy (self-hosted, ubuntu-20.04-x86-64)	9m 4s
cargo-clippy (self-hosted, ubuntu-20.04-x86-64)	9m 4s
cargo-clippy (self-hosted, ubuntu-20.04-x86-64)	9m 4s
cargo-test (self-hosted, ubuntu-20.04-x86-64)	18m 20s
cargo-test (self-hosted, ubuntu-20.04-x86-64)	18m 20s
cargo-test (self-hosted, ubuntu-20.04-x86-64)	18m 20s
cargo-test (self-hosted, ubuntu-20.04-x86-64)	18m 20s
cargo-clippy (self-hosted, macos-14-arm64)	10m 40s
cargo-clippy (self-hosted, macos-14-arm64)	10m 40s
cargo-clippy (self-hosted, macos-14-arm64)	10m 40s
cargo-clippy (self-hosted, macos-14-arm64)	10m 40s
cargo-clippy (self-hosted, windows-server-2022-x86-64)	18m 36s
cargo-clippy (self-hosted, windows-server-2022-x86-64)	18m 52s
cargo-clippy (self-hosted, windows-server-2022-x86-64)	19m 10s
cargo-clippy (self-hosted, windows-server-2022-x86-64)	19m 41s
cargo-test (self-hosted, macos-14-arm64)	24m 39s
cargo-test (self-hosted, macos-14-arm64)	24m 39s
cargo-test (self-hosted, macos-14-arm64)	24m 39s
cargo-test (self-hosted, macos-14-arm64)	24m 39s
cargo-test (self-hosted, windows-server-2022-x86-64)	19m 36s
cargo-test (self-hosted, windows-server-2022-x86-64)	19m 36s
cargo-test (self-hosted, windows-server-2022-x86-64)	19m 36s
cargo-test (self-hosted, windows-server-2022-x86-64)	19m 36s
	7h 15m 35s

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