Integrate TLS support into the server's connection accept path:
- Add SslServerAuthenticationOptions and TlsRateLimiter fields to NatsServer
- Extract AcceptClientAsync method for TLS negotiation, rate limiting, and
TLS state extraction (protocol version, cipher suite, peer certificate)
- Add InfoAlreadySent flag to NatsClient to skip redundant INFO when
TlsConnectionWrapper already sent it during negotiation
- Add TlsServerTests verifying TLS connect+INFO and TLS pub/sub
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