refactor(mrm_emergency_stop_operator): improve readability and change to read topic by polling

[Autumn60]

Description

Based on the discussion, change emergency_handler and mrm_handler to read topic by polling instead of best_effort callback.
In addition, readability was improved by reducing variable reuse.

Tests performed

psim test were performed

Effects on system behavior

nothing

Interface changes

nothing

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[Autumn60]

@mkuri
@TomohitoAndo

Could you review this PR as a code owner?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.

Project coverage is 28.63%. Comparing base (3d849e9) to head (2d35d5b).
Report is 1168 commits behind head on main.

Files	Patch %	Lines
...stop_operator/mrm_emergency_stop_operator_core.cpp	0.00%	14 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7313       +/-   ##
===========================================
+ Coverage   15.09%   28.63%   +13.53%     
===========================================
  Files        1967     1593      -374     
  Lines      135941   116056    -19885     
  Branches    42122    49470     +7348     
===========================================
+ Hits        20520    33227    +12707     
+ Misses      92700    73913    -18787     
+ Partials    22721     8916    -13805     

Flag	Coverage Δ		*Carryforward flag
differential	0.00% <0.00%> (?)
total	28.70% <ø> (+13.60%)	⬆️	Carriedforward from e84352f

*This pull request uses carry forward flags. Click here to find out more.

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