refactor: use QuickProxyNet for proxy negotiation

[milutinke]

What changed?

Replace UMPK's HTTP CONNECT, SOCKS4/SOCKS4a, and SOCKS5 handshake code with QuickProxyNet 3.0.0. The public proxy factories are unchanged. UMPK also overrides QuickProxyNet's abortive socket-close default so disposal still produces peer-observed EOF on macOS and other platforms.

The package version is now 0.9.0-beta.4.

Fixes #1.

Scope

All supported protocols (47 through 777). Proxy setup sits below the version-specific protocol code.

Validation

• All 11 proxy tests pass, including 20 consecutive runs of the EOF regression.
• A local proxy harness completed 70 tunnels across HTTP CONNECT, SOCKS4/SOCKS4a, and SOCKS5, with and without authentication. Bad credentials and cancellation were also tested.
• The merged full suite passes all 17 count gates, including 4,692 protocol tests.
• Release build, formatting, dataset verification, generated-file checks, packaging, and Native AOT tests pass.

The language-data check was not run because this worktree does not have the ignored MinecraftOfficial/downloads/1.8.9/server.jar prerequisite.

Notes for reviewers

There are no public API changes. QuickProxyNet accepts HTTP CONNECT status 200; the old code accepted any 2xx response.