Add metrics related to targeting/neuromodulation

[charlesbmi]

Describe the new feature or enhancement

User feedback: in addition to existing I_pa_target, would like peak/average-pressure-within-target.

Note: it would probably also be helpful to report the vector between the focal-point and the target center. i.e., how far off is the targeting?

Describe your proposed implementation

Describe how you think the feature or improvement should be implemented.
This can be added to the existing helper file: src/neurotechdevkit/results/_metrics.py