fix(client): parse Windows per-scheme proxies

[cyphercodes]

Fixes hyperium/hyper#4067.

Summary

• Parse Windows WinINET ProxyServer per-scheme values such as http=...;https=...;socks=....
• Apply socks= as a SOCKS fallback for both HTTP and HTTPS destinations while preserving explicit http=/https= entries and existing environment-derived values.
• Ignore unrelated per-scheme entries such as ftp= instead of treating the whole registry string as one proxy URI.

Tests

• cargo fmt --all --check
• cargo test --features client-proxy test_windows_proxy_server -- --nocapture
• cargo test --features client-proxy client::proxy::matcher::tests -- --nocapture
• cargo test --all-features client::proxy::matcher::tests -- --nocapture
• cargo check --target x86_64-pc-windows-gnu --features "client-proxy client-proxy-system"
• cargo test --all-features