test: add unit tests for core modules and integration tests for graceful shutdown

[Itsusinn]

Add comprehensive test coverage across wind-core (utils, resolve,
dispatcher), wind-socks (lib, udp), wind-dns (resolver), wind-base
(resolve, direct), and a new wind-test shutdown module.

wind-core

• utils: StackPrefer (from_str/serde round-trip/aliases) + is_private_ip boundary cases (19 tests)
• resolve: pick/filter_addrs_by_preference all 4 preference modes, empty input, order preservation (16 tests)
• dispatcher: AclRouter edge cases: SRC-PORT, IN-PORT, DOMAIN-KEYWORD, DOMAIN-REGEX, DOMAIN-WILDCARD (5 tests)

wind-socks

• lib: convert_addr/convert_to_socks_addr round-trip for IPv4/IPv6/Domain (9 tests)
• udp: parse_udp_request_sync SOCKS5 UDP header (all ATYP, RSV errors, truncation), target_addr_to_socket, unmap_v4_mapped (14 tests)

wind-dns

• resolver: parse_server scheme/port/IPv6-bracket/SNI combos, split_host_port (14 tests)

wind-base

• resolve: resolve_target with mock Resolver — verifies bypass on IP inputs (3 tests)
• direct: DirectOutboundOpts construction (3 tests)

wind-test (new shutdown.rs module)

Graceful shutdown integration tests:

• SOCKS5 listen loop exits promptly on cancel
• Raw TCP relay in-flight connection still relays after cancel
• TUIC QUIC listen loop stops on ctx.token.cancel()
• TUIC in-flight relay disconnects on cancel (documents current behaviour)
• TaskTracker drain completes within timeout

Signed-off-by: iHsin sun@ihsin.dev
Assisted-by: OpenClaw:deepseek-v4-flash