Avoid boxing in DefaultConnector chain #2591

Job	Run time
build_versions (stable)	11s
build_versions (beta)	18s
Test	39s
build_versions (1.71.1)	17s
Test	40s
cargo-deny (aarch64-apple-ios)	20s
Test (charset)	33s
Test (charset)	45s
cargo-deny (aarch64-linux-android)	18s
Test (cookies)	44s
Test (cookies)	39s
Docs	1m 30s
cargo-deny (i686-pc-windows-gnu)	18s
Test (socks-proxy)	40s
Test (socks-proxy)	44s
cargo-deny (i686-pc-windows-msvc)	17s
Test (gzip)	29s
Test (gzip)	43s
Lint	18s
cargo-deny (i686-unknown-linux-gnu)	17s
Test (brotli)	44s
Test (brotli)	57s
cargo-deny (wasm32-unknown-unknown)	19s
Test (json)	31s
Test (json)	41s
Test (native-tls)	36s
cargo-deny (x86_64-apple-darwin)	17s
Test (native-tls)	47s
cargo-deny (x86_64-apple-ios)	18s
cargo-deny (x86_64-pc-windows-gnu)	21s
cargo-deny (x86_64-pc-windows-msvc)	19s
cargo-deny (x86_64-unknown-linux-gnu)	20s
cargo-deny (x86_64-unknown-redox)	18s
	17m 8s

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