fix(autoware_multi_object_tracker): measure latency with latest detection update time

[technolojin]

Description

Fixing the pipeline latency measurement point.
The latest updated detection time will be used for the latency measurement.

1. startMeasurementTime uses latest time rather than oldest time
2. object_oldest_time is renamed to object_earliest_time
3. onMessage method is removed since it is not callback function anymore.

Related links

Parent Issue: #9428

• Link

How was this PR tested?

Notes for reviewers

None.

Interface changes

None.

Effects on system behavior

None.

[github-actions]

Thank you for contributing to the Autoware project!

🚧 If your pull request is in progress, switch it to draft mode.

Please ensure:

• You've checked our contribution guidelines.
• Your PR follows our pull request guidelines.
• All required CI checks pass before marking the PR ready for review.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Project coverage is 29.49%. Comparing base (557a8b5) to head (a888295).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...lti_object_tracker/src/processor/input_manager.cpp	0.00%	9 Missing ⚠️
...i_object_tracker/src/multi_object_tracker_node.cpp	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9533      +/-   ##
==========================================
- Coverage   29.49%   29.49%   -0.01%     
==========================================
  Files        1443     1443              
  Lines      108648   108654       +6     
  Branches    41537    41540       +3     
==========================================
  Hits        32047    32047              
- Misses      73479    73485       +6     
  Partials     3122     3122              

Flag	Coverage Δ		*Carryforward flag
differential	0.00% <0.00%> (?)
total	29.50% <ø> (+<0.01%)	⬆️	Carriedforward from 557a8b5

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[cyn-liu]

I have tested this PR and the result looks consistent with expectations.
#9428 (comment)