v0.2.53

v0.2.53 — SDL_net resolver IPv6/literal-IP fix

Pulled SDL_net docs + source after v0.2.52. Found root cause: vendored
SDL_net's ResolveAddress calls getaddrinfo with hints=NULL —
AF_UNSPEC (queries A+AAAA) and no AI_NUMERICHOST (DNS path even for
literal IPs). On Windows boxes with IPv6 enabled but no IPv6
connectivity (common consumer ISP setup), the AAAA query stalls the
resolver thread. Our UDP STUN already uses AF_INET hint and works
universally — same fix applied here.

Patch to vendored SDL_net.c ResolveAddress:

• hints.ai_family = AF_INET (forces IPv4, skips AAAA stall)
• hints.ai_flags |= AI_NUMERICHOST when input is a literal IPv4
  (instant short-circuit, no DNS query)

Safe because we're IPv4-only project-wide. Single-function change,
no API surface change. Benefits ConnectUpstream (spec's TCP dial
to host's listener after JOIN_ACK) which still uses SDL_net's
resolver.

v0.2.52's raw winsock TCP-STUN stays in place. Unit tests 63/63.