Beta-6 Target Pose interpolation does not work with alliance flipping

[bhall-ctre]

Describe the bug
When the shouldFlipPath boolean supplier returns true, the target pose interpolation does not work. The behavior is that PathPlanner appears to be interpolating in the direction of the original unflipped path.

To Reproduce
Steps to reproduce the behavior:

1. Update our SwerveWithPathPlanner example to PathPlanner beta-6.
2. In configureAutoBuilder(), add a logger for the target pose callback:

var targetPoseLogger = NetworkTableInstance.getDefault().getStructTopic("Target Pose", Pose2d.struct).publish();
PathPlannerLogging.setLogTargetPoseCallback(targetPoseLogger);

3. Run the project in simulation.
4. Set the alliance to Blue (while "Disconnected") and run autonomous. Use the AdvantageScope Odometry tab to view the "Target Pose" field (use the Connect to Simulator feature).
5. Set the alliance to Red (while "Disconnected") and re-run autonomous. Use the AdvantageScope Odometry tab to view the "Target Pose", and note the incorrect behavior.

Expected behavior
The behavior on the Red alliance should match the Blue alliance, just flipped.

Screenshots
Below is a zip with a video of the correct (blue) and incorrect (red) behavior.
PathPlanner-beta-6-bug.zip

Versions: (please complete the following information):

• OS: Windows 11
• GUI Version: n/a
• PPLib Version: 2025.0.0-beta-6
• PPLib Language: Java, C++, Python

Additional context
This issue was likely introduced with the changes in #935.

[mjansen4857]

Yeah, the heading doesn’t get flipped which is now used for interpolation. Oversight on my part. Will try to get fix out asap.