feat(diagnostic_converter): remove unit and blank in the value

[takayuki5168]

Description

Removed the unit and the blank if they exist in the value of diagnostics.

I confirmed that diagnostics with the unit works well with the scenario simulator v2 via diagnostic_converter.

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[kyoichi-sugahara]

LGTM

[codecov]

Codecov Report

Patch coverage: 50.00% and no project coverage change.

Comparison is base (cf753f4) 13.14% compared to head (c8e599b) 13.14%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3151   +/-   ##
=======================================
  Coverage   13.14%   13.14%           
=======================================
  Files        1239     1239           
  Lines       87524    87535   +11     
  Branches    26744    26750    +6     
=======================================
+ Hits        11502    11509    +7     
- Misses      63871    63872    +1     
- Partials    12151    12154    +3     

Flag	Coverage Δ		*Carryforward flag
differential	37.11% <50.00%> (?)
total	13.14% <ø> (+<0.01%)	⬆️	Carriedforward from cf753f4

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

Impacted Files	Coverage Δ
...luator/diagnostic_converter/src/converter_node.cpp	58.33% <50.00%> (+2.33%)	⬆️

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