Use the new declare_or_get_parameter API for nav2_regulated_pure_pursuit_controller

[song6-1]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	#5299
Primary OS tested on	Ubuntu
Robotic platform tested on	N/A
Does this PR contain AI generated software?	No
Was this PR description generated by AI software?	N/A

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Description of contribution in a few bullet points

Updated the parameter_handler in nav2_regulated_pure_pursuit_controller to use declare_or_get_param

Description of documentation updates required from your changes

N/A

Description of how this change was tested

Performed linting validation using pre-commit run --all and testing locally using colcon test

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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-*.