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.
Fix setMark early-return conditions that were inverted relative to
Linux: on FreeBSD (SO_USER_COOKIE) and OpenBSD (SO_RTABLE), a
non-zero mark was short-circuited instead of applied, disabling
socket marking entirely.
Also fix GetClientIP to trim leading whitespace from X-Forwarded-For
entries (per RFC 7239), and fix Body.Read to subtract len(b) instead
of n from recordSize when a single read exceeds the remaining quota.
Add unit tests for internal/net/ (addr, dialer, http, ip, net, pipe,
transport, resolve, proxyproto, udp).
ginuerzh