[ENH] TorchBiphasicAxonMapSpatial

[HououinKyouma-2036]

Description

Implemented TorchBiphasicAxonMapSpatial class with constructor and forward function.

Modified predict_percept and relavent methods.

BiphasicsAxonMapSpatial now allows for self.engine to be torch, on top of jax, cython, and serial.

Closes #615

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation change

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

For detailed information on these and other aspects, see the contribution guidelines: https://pulse2percept.readthedocs.io/en/latest/developers/contributing.html