refactor(tuic-core): replace manual byte parsing with nom streaming parsers

[Itsusinn]

Summary

Replace the two sets of hand-written byte-parsing code (free helpers + tokio-util Decoder impls) with a single set of nom 8 streaming parsers.

Problem

tuic-core maintained two parallel parsing implementations — free helper functions (decode_header, decode_command, decode_address) and tokio-util Decoder/Encoder codecs — with identical parsing logic but different error contracts. The comment explicitly warned "Any change to the on-wire format MUST be mirrored across both implementations."

Solution

Define a single set of nom streaming parsers:

Parser	Input	Output
parse_header	&[u8]	(&[u8], Header)
parse_command_body	&[u8]	(&[u8], Command)
parse_address	&[u8]	(&[u8], Address)

Both paths call the same parsers, differing only in how nom::Err::Incomplete is mapped:

• Codec path: Incomplete → Ok(None) (tokio-util contract)
• Free helpers: Incomplete → Err(eyre!("Incomplete data in ..."))

Encoder implementations are unchanged (nom is parsing-only).

Changes

• Cargo.toml — add nom = "8"
• src/proto/mod.rs — core parsers + nom_parse() wrapper + updated free helpers; ~110 lines of manual parsing deleted
• src/proto/header.rs — HeaderCodec::decode calls parse_header
• src/proto/cmd.rs — CmdCodec::decode calls parse_command_body
• src/proto/addr.rs — AddressCodec::decode calls parse_address

Verification

• All 18 tuic-core unit tests pass
• All downstream crates (wind-tuic, wind-tuiche, tuic-tests) compile without changes
• tuic-tests protocol and integration tests pass
• Clippy clean (zero warnings)

6 files changed, 183 insertions(+), 277 deletions(-)