Handle MCCP1 non-standard SB terminator, fix nanvaent connection

[powerje]

Summary

• MCCP1 (option 85) uses a non-standard SB start sequence: IAC SB 85 WILL SE where SE appears without a preceding IAC. Our skipSB only recognized IAC SE, so the MCCP1 start marker was treated as an incomplete subnegotiation and buffered in telbuf — swallowing all subsequent data including the login banner.
• Adds MCCP1 constant (option 85) and a TeloptPattern to recognize and skip the 5-byte MCCP1 start sequence.
• Adds nanvaent.org replay tests using captured bytes to verify MCCP2 decompression with standard zlib (windowBits=15) and embedded telnet commands in the compressed stream.

Test plan

• nanvaentNegotiationAndMCCP2 — full replay of nanvaent's negotiation (split packets), verifies MSSP reception and banner text
• nanvaentCombinedMCCP2Packet — same replay with coalesced MCCP2 + compressed packet
• nanvaentInflateStreamDirectly — verifies InflateStream handles standard zlib format
• All 142 existing tests still pass