[RPP] Prevent collision check premature termination

[EricoMeger]

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	#5595
Primary OS tested on	Ubuntu 24.04
Robotic platform tested on	Physical Robot (differential-drive)
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

• Fixes a bug in RPP where the robot would "creep" forward after stopping for an obstacle if min_lookahead was set lower than min_distance_to_obstacle
• Change isCollisionImminent logic to always cover at least up to min_distance_to_obstacle, even when carrot_dist shrinks.

Description of documentation updates required from your changes

None

Description of how this change was tested

Tested for a week on a physical differential-drive robot using a 270-degree LiDAR in a real-world environment. The tests included various routes with both static and dynamic obstacles placed in the robot's path. No negative side effects or degradation in general navigation behavior were observed.

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Future work that may be required in bullet points

I don't like to create a entire new variable just that it receives carrot_dist if min_distance_to_obstacle is unused, but I can't think of a better way to do that. I'm open to suggestions.

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]

Just a nit for wording, LGTM. Check out the CI issues, it looksl ike you have linting violations that need to be resolved before merge

@doisyg please approve as well

[EricoMeger]

Just updated the title to add the [RPP] prefix, to make the PR more self-explanatory

[mergify]

@EricoMeger, your PR has failed to build. Please check CI outputs and resolve issues.
You may need to rebase or pull in main due to API changes (or your contribution genuinely fails).