Make Duration::not_zero public. #2805

Job	Run time
build_versions (stable)	17s
build_versions (beta)	16s
Test	1m 3s
cargo-deny (aarch64-apple-ios)	17s
Test (charset)	1m 4s
build_versions (1.71.1)	16s
Test	1m 1s
cargo-deny (aarch64-linux-android)	21s
cargo-deny (i686-pc-windows-gnu)	17s
Test (charset)	1m 1s
Docs	1m 57s
Test (cookies)	1m 4s
cargo-deny (i686-pc-windows-msvc)	21s
Test (socks-proxy)	58s
cargo-deny (i686-unknown-linux-gnu)	18s
Test (gzip)	51s
cargo-deny (wasm32-unknown-unknown)	24s
Lint	36s
Test (cookies)	1m 14s
Test (brotli)	50s
cargo-deny (x86_64-apple-darwin)	19s
Test (socks-proxy)	1m 5s
Test (json)	53s
cargo-deny (x86_64-apple-ios)	25s
Test (gzip)	1m 2s
Test (native-tls)	1m 2s
Test (brotli)	59s
cargo-deny (x86_64-pc-windows-gnu)	21s
Test (rustls-no-provider)	1m 9s
Test (json)	1m 2s
cargo-deny (x86_64-pc-windows-msvc)	19s
Test (native-tls)	1m 12s
cargo-deny (x86_64-unknown-linux-gnu)	17s
cargo-deny (x86_64-unknown-redox)	18s
	24m 49s

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