[mppi] fix division by zero, clean raw pointers code

[adivardi]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	-
Primary OS tested on	Ubuntu
Robotic platform tested on	gazebo simulation & real robot
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

fix division by zero in constraint_critic, leading to cost values being NaNs. These values then propagate through all the critics and results in NaN control_sequence. These NaNs were removed by the hard applyControlSequenceConstraints(), but replaced with ax_max & wz_max. These lead to high turning at the start of a run.

Before the change:
https://github.com/user-attachments/assets/d43f7455-e8b7-4bd6-a8b1-12326bd4ce2b

After the change:
https://github.com/user-attachments/assets/31c06d84-6bec-4b57-bbee-d7d33f944515

Also, a minor change in applyConstraints() to use Eigen Array operations instead of loop and raw pointers. No functional change.

Description of documentation updates required from your changes

None

Description of how this change was tested

• Tested on simulation and on robot
• Manually inspected the cost values and control_sequence.wz

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Future work that may be required in bullet points

None

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
...ler/include/nav2_mppi_controller/motion_models.hpp	100.00% <100.00%> (ø)
..._mppi_controller/src/critics/constraint_critic.cpp	65.21% <ø> (ø)

... and 3 files with indirect coverage changes

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[SteveMacenski]

Nice, love it thanks!