remove mutex

[qicosmos]

remove mutex in connection.

[github-actions]

Code Coverage Report
for detail, goto summary download Artifacts

Filename                    Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
client_util.hpp                     3                 1    66.67%          19                 8    57.89%           2                 1    50.00%
codec.h                             4                 0   100.00%          24                 2    91.67%           0                 0         -
connection.h                       37                 6    83.78%         360                94    73.89%          70                36    48.57%
io_service_pool.h                   5                 0   100.00%          32                 1    96.88%          12                 1    91.67%
md5.hpp                            19                 2    89.47%         127                 8    93.70%          24                 0   100.00%
nonstd_any.hpp                     20                 5    75.00%          49                12    75.51%           8                 4    50.00%
router.h                           19                 2    89.47%         144                35    75.69%           4                 3    25.00%
rpc_client.hpp                     73                12    83.56%         663               152    77.07%         132                62    53.03%
rpc_server.h                       26                 3    88.46%         191                20    89.53%          40                 9    77.50%
string_view.hpp                    23                10    56.52%          72                35    51.39%          22                14    36.36%
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                             229                41    82.10%        1681               367    78.17%         314               130    58.60%