nav2_route vizualization marker rendering performance improvement

[emersonknapp]

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	(add tickets here #1)
Primary OS tested on	Ubuntu
Robotic platform tested on	Gazebo simulation of Polymath autonomy
Does this PR contain AI generated software?	No
Was this PR description generated by AI software?	No

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Description of contribution in a few bullet points

Route graph visualization marker rendering performance improvement. Doesn't change end behavior.

• Use SPHERE_LIST for all of the nodes
• Use LINE_LIST for all of the edges
• Keep the text IDs the same, but put them in separate namespaces for separate visibility toggling

Description of documentation updates required from your changes

None

Description of how this change was tested

Future work that may be required in bullet points

N/A

For Maintainers:

• Check that any new parameters added are updated in docs.nav2.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists
• Should this be backported to current distributions? If so, tag with backport-*.

[SteveMacenski]

A test fails:

- nav2_route.UtilsTest test_to_visualization_msg_conversion (/opt/overlay_ws/src/navigation2/nav2_route/test/test_utils_and_types.cpp:132)
  <<< failure message
    /opt/overlay_ws/src/navigation2/nav2_route/test/test_utils_and_types.cpp:162
    Expected equality of these values:
      graph_msg.markers.size()
        Which is: 19
      34u
        Which is: 34
  >>>

[emersonknapp]

@SteveMacenski fixed unit test and addressed review comment

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
nav2_route/include/nav2_route/utils.hpp	100.00% <100.00%> (+1.14%)	⬆️

... and 3 files with indirect coverage changes

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