Fix duplicate poses with computePlanThroughPoses

[tonynajjar]

---

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	(add tickets here #1)
Primary OS tested on	(Ubuntu, MacOS, Windows)
Robotic platform tested on	(Steve's Robot, gazebo simulation of Tally, hardware turtlebot)
Does this PR contain AI generated software?	(No; Yes and it is marked inline in the code)
Was this PR description generated by AI software?	Out of respect for maintainers, AI for human-to-human communications are banned

Story:

1- I turned on MPPI's enforce_path_inversion and noticed that the pruned path was flake-ly being cut short to one of the poses that were used to generate the global plan with computePlanThroughPoses
2- I put my investigation hat and found out that in MPPI's findFirstPathInversion, the dot_product was sometimes -0.0000000(peanuts) -> negative -> path inversion. Turns out points in points OAB, B was sometimes very slightly before A so the vector was pointing in the other direction.
3- Looking into the planner server, computePlanThroughPoses does start the concatenated path exactly where the first one ends and thus this PR.

I think I experienced a similar issue in the past with RPP but can't find the conversation

---

Description of contribution in a few bullet points

• Change computePlanThroughPoses to skip the first pose of the paths to concatenate

Description of documentation updates required from your changes

Description of how this change was tested

No more early false positive inversion points

---

Future work that may be required in bullet points

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-*.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
nav2_planner/src/planner_server.cpp	92.92% <100.00%> (+0.06%)	⬆️

... and 8 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.