Fix QuestProgressExtended packet header overflow (C1 to C2)

[Mosch0512]

The QuestProgressExtended packet (0xF6, 0x0C) is 272 bytes but was declared with a C1 header. A C1 header stores its length in a single byte, so it cannot represent sizes above 255: the length was written as 272 & 0xFF = 16. Clients therefore framed only 16 bytes, the remaining 256 desynced the packet stream, and the connection dropped when a quest was started or its progress was shown.

Switch the header to C2HeaderWithSubCode, matching the identically sized QuestStateExtended packet and every other server packet larger than 255 bytes. The 2-byte C2 length encodes 272 correctly. Field offsets are unchanged; the generated struct definitions are updated to match the packet definition.

This is the server part for sven-n/MuMain#425

Closes #779

[gemini-code-assist]

Summary of Changes

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This pull request addresses a packet stream desync issue caused by an overflow in the QuestProgressExtended packet header. By switching from a single-byte C1 header to a two-byte C2 header, the system can now correctly handle the 272-byte packet size, preventing connection drops during quest updates.

Highlights

• Packet Header Migration: Migrated the QuestProgressExtended packet from a C1 header to a C2 header to support packet sizes exceeding 255 bytes.
• Struct Definition Updates: Updated the packet definition and generated C# structs to utilize C2HeaderWithSubCode, ensuring correct length encoding for the 272-byte packet.

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[gemini-code-assist]

Code Review

This pull request updates the QuestProgressExtended packet and its reference counterpart to use the C2HeaderWithSubCode (header type 0xC2) instead of C1HeaderWithSubCode (header type 0xC1). This changes the packet length representation from a byte to a ushort, allowing for larger packet sizes. There are no review comments, and I have no additional feedback to provide.