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