抽出readMessage函数，方便对该函数单独benchmark

[guonaihong]

No description provided.

[codecov-commenter]

Codecov Report

Patch coverage: 91.83% and project coverage change: -0.35% ⚠️

Comparison is base (3842c68) 81.79% compared to head (17c7516) 81.44%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #15      +/-   ##
==========================================
- Coverage   81.79%   81.44%   -0.35%     
==========================================
  Files          13       13              
  Lines         791      787       -4     
==========================================
- Hits          647      641       -6     
- Misses         91       92       +1     
- Partials       53       54       +1     

Files Changed	Coverage Δ
server_handshake.go	68.88% <ø> (ø)
server_options.go	100.00% <ø> (ø)
conn.go	84.09% <91.83%> (-0.99%)	⬇️

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