Fix the problem that cannot send object bi-directionally

[tetter27]

• Fixed the problem caused by holding client mutex in handle_incoming_uni_stream
• Removed unnecessary mutable for the client

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 65.55%. Comparing base (39e9134) to head (3c64e13).

Additional details and impacted files

@@             Coverage Diff              @@
##           draft-06     #127      +/-   ##
============================================
+ Coverage     65.52%   65.55%   +0.02%     
============================================
  Files            62       62              
  Lines          3104     3106       +2     
============================================
+ Hits           2034     2036       +2     
  Misses         1070     1070              

Components	Coverage Δ
moqt-core	91.45% <ø> (ø)
moqt-server	53.57% <0.00%> (+0.04%)	⬆️