Avoid boxing in DefaultConnector chain #2602

Job	Run time
build_versions (stable)	2m 33s
build_versions (beta)	2m 51s
Lint	17s
build_versions (1.71.1)	2m 46s
Test	41s
cargo-deny (aarch64-apple-ios)	19s
Test (charset)	41s
cargo-deny (aarch64-linux-android)	18s
Test	29s
Test (cookies)	47s
cargo-deny (i686-pc-windows-gnu)	20s
Test (charset)	29s
Docs	1m 25s
Test (socks-proxy)	42s
cargo-deny (i686-pc-windows-msvc)	19s
Test (cookies)	35s
cargo-deny (i686-unknown-linux-gnu)	20s
Test (socks-proxy)	32s
Test (gzip)	31s
cargo-deny (wasm32-unknown-unknown)	18s
cargo-deny (x86_64-apple-darwin)	19s
Test (gzip)	40s
Test (brotli)	36s
Test (brotli)	40s
Test (json)	32s
Test (json)	42s
Test (native-tls)	42s
Test (native-tls)	47s
cargo-deny (x86_64-apple-ios)	18s
cargo-deny (x86_64-pc-windows-gnu)	20s
cargo-deny (x86_64-pc-windows-msvc)	20s
cargo-deny (x86_64-unknown-linux-gnu)	17s
cargo-deny (x86_64-unknown-redox)	19s
	23m 45s

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