[BtActionNode] [BtServiceNode] clear between calls

[doisyg]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses
Primary OS tested on	Ubuntu 24.04
Robotic platform tested on	Dexory robot
Does this PR contain AI generated software?	No

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Description of contribution in a few bullet points

In BtActionNode and BtServiceNode, the goal_, result_ and request_ objects were not cleared between 2 calls. Hence keeping an old value if any field of these was not explicitly set by a BT node inheriting BtActionNode or BtServiceNode.
I realized it while using ComputePathToPose and not understanding why the action was using a previous start pose when actually making a new call without a start parameter (where it is expected that the current pose of the robot will be used):

navigation2/nav2_behavior_tree/plugins/action/compute_path_to_pose_action.cpp

Lines 33 to 38 in 447c8ce

	getInput("goal", goal_.goal);
	getInput("planner_id", goal_.planner_id);
	if (getInput("start", goal_.start)) {
	goal_.use_start = true;
	}
	}

This PR reinitializes goal_, result_ and request_ between calls to solve this issue.

Description of documentation updates required from your changes

Description of how this change was tested

• Appropriate behavior of ComputePathToPose when calling it successively with and without a valid input start

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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

[SteveMacenski]

Nice! I checked and see no problems with it. I thought maybe some node maintained state, but it doesn't appear so