middleware/doc: use Relaxed atomics for single-variable counter #2890

Job	Run time
build_versions (stable)	8s
build_versions (beta)	15s
Test	57s
Test	39s
build_versions (1.71.1)	14s
Test (charset)	53s
cargo-deny (aarch64-apple-ios)	24s
Test (charset)	44s
Test (cookies)	1m 4s
cargo-deny (aarch64-linux-android)	21s
Test (cookies)	57s
Docs	1m 41s
Test (socks-proxy)	56s
Test (socks-proxy)	43s
cargo-deny (i686-pc-windows-gnu)	24s
Test (gzip)	53s
cargo-deny (i686-pc-windows-msvc)	19s
Test (gzip)	43s
Test (brotli)	51s
cargo-deny (i686-unknown-linux-gnu)	20s
Test (brotli)	43s
Lint	30s
Test (json)	3m 0s
Test (json)	43s
cargo-deny (wasm32-unknown-unknown)	19s
Test (native-tls)	55s
Test (native-tls)	51s
cargo-deny (x86_64-apple-darwin)	21s
Test (rustls-no-provider)	1m 2s
cargo-deny (x86_64-apple-ios)	28s
cargo-deny (x86_64-pc-windows-gnu)	24s
cargo-deny (x86_64-pc-windows-msvc)	20s
cargo-deny (x86_64-unknown-linux-gnu)	24s
cargo-deny (x86_64-unknown-redox)	20s
	23m 46s

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