refactor(perception_util): refactor moving unnamed namespace from include file to src file

[scepter914]

Description

Move unnamed namespace from include file to src file, which is reviewed by #1954 (comment).

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[codecov]

Codecov Report

Base: 10.42% // Head: 10.39% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (c689587) compared to base (d707d2b).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2028      +/-   ##
==========================================
- Coverage   10.42%   10.39%   -0.03%     
==========================================
  Files        1169     1167       -2     
  Lines       83517    83573      +56     
  Branches    19552    19549       -3     
==========================================
- Hits         8705     8690      -15     
- Misses      65308    65381      +73     
+ Partials     9504     9502       -2     

Flag	Coverage Δ		*Carryforward flag
differential	5.86% <ø> (?)
total	10.41% <ø> (+<0.01%)	⬆️	Carriedforward from 61f3767

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

Impacted Files	Coverage Δ
...planning_evaluator/src/planning_evaluator_node.cpp	37.11% <0.00%> (-1.04%)	⬇️
...autoware_utils/test/src/geometry/test_geometry.cpp	42.87% <0.00%> (-0.47%)	⬇️
...include/tier4_autoware_utils/geometry/geometry.hpp	95.62% <0.00%> (-0.19%)	⬇️
planning/obstacle_cruise_planner/src/node.cpp	0.00% <0.00%> (ø)
.../rtc_manager_rviz_plugin/src/rtc_manager_panel.cpp	0.00% <0.00%> (ø)
.../rtc_manager_rviz_plugin/src/rtc_manager_panel.hpp	0.00% <0.00%> (ø)
.../obstacle_cruise_planner/src/planner_interface.cpp	0.00% <0.00%> (ø)
...ed_object_validation/src/object_lanelet_filter.cpp	0.00% <0.00%> (ø)
...include/obstacle_avoidance_planner/utils/utils.hpp	0.00% <0.00%> (ø)
...lugin_autogen/UVLADIE3JM/moc_rtc_manager_panel.cpp	0.00% <0.00%> (ø)
... and 11 more

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