refactor(network): optimized client mem usage

[xiaost]

Use Read() instead of Peek()+Skip() in ReadByte() and appendBodyFixedSize()
to avoid holding references to the underlying buffer. Peek() returns slices
that reference the internal buffer, preventing it from being released or
reused until the reference is dropped.

Also updated cloudwego/gopkg dependency and moved connstate import to
gopkg/net/connstate.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.25%. Comparing base (bf7ec5b) to head (52be57c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1483      +/-   ##
==========================================
+ Coverage   86.22%   86.25%   +0.02%     
==========================================
  Files         148      148              
  Lines       14157    14158       +1     
==========================================
+ Hits        12207    12212       +5     
+ Misses       1417     1416       -1     
+ Partials      533      530       -3     

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