When no custom resolver or host mapper is configured, xnet.Resolve now
resolves hostnames via Go's native pure-Go resolver (PreferGo: true)
instead of returning the hostname unchanged.
Previously, the unresolved hostname would reach net.Dialer.DialContext,
which on CGO_ENABLED=1 builds used cgo-based DNS — blocking a dedicated
OS thread per concurrent lookup. At scale (1000+ listeners), this
exhausted Go's 10000-thread limit.
Fixesgo-gost/gost#550
matcher: fix IPv6 normalization via netip.ParseAddr, port-range overwrite
by switching to []*PortRange map, case-insensitive domain/host matching,
glob.MustCompile→Compile to avoid panic on invalid patterns.
plugin: guard nil *Options in NewGRPCConn and NewHTTPClient; add
HTTPClientTransport helper for idle-connection cleanup.
net/*: add doc comments for all exported symbols (no code changes).
Add 30 tests (matcher_test.go 22, plugin_test.go 8) covering all
matcher types, nil safety, case insensitivity, IPv6 normalization,
port ranges, and plugin option composition.
ginuerzh