fix: accept unimplemented socket options, bump 0.3.0

[danbugs]

Summary

• Fix DNS resolution regression introduced in v0.2.0 (PR refactor: remove dead code, fix silent socket option no-ops, fix tempdir leak #37)
• Bump version to 0.3.0

Root cause

The v0.2.0 setsockopt/getsockopt hardening changed silent no-ops
into errors for unrecognised socket options. This broke DNS resolution
because musl's resolver sets IP_RECVERR (IPPROTO_IP=0, optname=11)
on its UDP socket and aborts when the setsockopt call fails.

Traced via HL_DISPATCH_DEBUG=1 — the very first thing after
net_socket is net_setsockopt(level=0, optname=11, value=1), which
returned an error and caused the guest to close the socket immediately.

Fix

Revert setsockopt to accepting unknown options silently and
getsockopt to returning 0 for unknown options. For a socket-proxy
pattern, the guest OS manages its own socket semantics — unknown
options are harmless configuration hints, not security boundaries.
Known options (SO_REUSEADDR, SO_KEEPALIVE, TCP_NODELAY) are
still applied to the host socket.

Test plan

• cargo test --lib passes on Linux (46/46) and Windows (38/38)
• cargo clippy --all-targets -- -D warnings clean on both platforms
• networking-py urllib_get passes locally with the fix (was failing with v0.2.0)
• CI: all checks green including networking-py runtime tests

[github-actions]

Linux Benchmarks

Details

Benchmark suite	Current: fe6972d	Previous: cb048d7	Ratio
hello_world (median)	20 ms	20 ms	1
pandas (median)	100 ms	100 ms	1
density (per VM)	7 MB	7 MB	1
snapshot (disk)	385 MiB	385 MiB	1

This comment was automatically generated by workflow using github-action-benchmark.

[github-actions]

Windows Benchmarks

Details

Benchmark suite	Current: fe6972d	Previous: cb048d7	Ratio
hello_world (median)	260 ms	218 ms	1.19
pandas (median)	840 ms	739 ms	1.14
density (per VM)	6 MB	6 MB	1
snapshot (disk)	393 MiB	393 MiB	1

This comment was automatically generated by workflow using github-action-benchmark.