feat: add heartbeat MessageType and processing logic for svrTransHandler

[DMwangnima]

What type of PR is this?

feat: For implementing server-side Hessian2 codec heartbeat logic, we need to introduce Heartbeat MessageType. This heartbeat logic belongs to framework and user could not perceive it.
This change does not effect other codecs.

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[codecov]

Codecov Report

Patch coverage: 61.11% and project coverage change: -0.07% ⚠️

Comparison is base (645fec2) 69.09% compared to head (133e44a) 69.03%.

❗ Current head 133e44a differs from pull request most recent head 4d44bb1. Consider uploading reports for the commit 4d44bb1 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1069      +/-   ##
===========================================
- Coverage    69.09%   69.03%   -0.07%     
===========================================
  Files          252      252              
  Lines        18813    18815       +2     
===========================================
- Hits         12999    12988      -11     
- Misses        4632     4639       +7     
- Partials      1182     1188       +6     

Files Changed	Coverage Δ
pkg/remote/message.go	88.03% <ø> (ø)
pkg/remote/trans/default_server_handler.go	74.59% <61.11%> (-1.23%)	⬇️

... and 5 files with indirect coverage changes

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