Expose iSWAP per-drive predefined-position readers + rotation drive axis accessors

[BioCam]

This is a crucial step in the "Tame the iSWAP" project (part 4):
accessing the positional information that the iSWAP uses for its firmware-level positioning.

Summary

Adds 5 new public methods on STARBackend for iSWAP introspection.

Predefined-position table readers (one per drive, all read R0 RA):

• request_iswap_rotation_drive_predefined_positions()
• request_iswap_wrist_drive_predefined_positions()
• request_iswap_gripper_predefined_positions()

Each returns a Dict[str, Union[int, float]] with semantic keys that mirror the existing RotationDriveOrientation / WristDriveOrientation enums:

>>> await star.request_iswap_rotation_drive_predefined_positions()
{'home': 13000, 'left': -29007, 'front': 156, 'right': 29068,
 'parking': 29500, 'extra_1': 29068, 'extra_2': 29068, 'extra_3': 29068,
 'extra_4': 29068, 'link_1_len': 137.8}

>>> await star.request_iswap_wrist_drive_predefined_positions()
{'home': -26577, 'right': -26577, 'straight': -8860, 'left': 9044,
 'reverse': 26858, 'parking': -26577, 'extra_1': -26577, 'extra_2': -26577,
 'extra_3': -26577, 'link_2_len': 137.7}

>>> await star.request_iswap_gripper_predefined_positions()
{'home': 13100, 'fully_open': 24120, 'closed': 12960,
 'plate_type_1': 12780, 'plate_type_2': 13100, ...,
 'plate_type_7': 13100}

...which will be crucial for the next step 👀

Rotation drive single-axis accessors (deck coordinates, mm):

• iswap_rotation_drive_request_x()
• iswap_rotation_drive_request_z()

Lets callers grab one axis without paying for a full Coordinate query.
Existing iswap_rotation_drive_request_position() simplified to a 4-line composite using the x / y / z accessors.

Internal reorganization (no API impact)

Pre-existing iSWAP-related methods now grouped into three section headers:

# iSWAP: Rotation Drive (Joint 1)
# iSWAP: Wrist Drive (Joint 2)
# iSWAP: Gripper

Each section opens with the drive's exposed constants:

• iswap_<drive>_drive_min_increment / _max_increment (encoder bounds)
• iswap_<drive>_drive_<unit>_per_increment (resolution: deg for rotation/wrist, mm for gripper)

The orientation classifiers (request_iswap_rotation_drive_orientation, request_iswap_wrist_drive_orientation) now reference the exposed resolution constants by name instead of magic-numbering the deg/incr factor.

No breaking changes

All 282 of STARBackend's pre-existing methods preserved.
Diff is purely additive (5 new methods) plus internal reorganization (existing methods moved into per-drive sections without any signature change).

[Copilot]

Pull request overview

This PR extends STARBackend with additional iSWAP introspection APIs to read per-drive predefined-position tables (EEPROM via R0 RA) and to query rotation-drive X/Z axes directly, while reorganizing iSWAP-related methods into per-drive sections.

Changes:

• Add EEPROM predefined-position table readers for iSWAP rotation drive (W), wrist drive (T), and gripper drive (G).
• Add rotation-drive single-axis accessors (iswap_rotation_drive_request_x(), iswap_rotation_drive_request_z()) and simplify the composite XYZ accessor.
• Reorganize iSWAP code into drive-specific sections and expose drive constants (bounds/resolution).

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[rickwierenga]

ideally this would be named iswap_rotation_drive_request_predefined_positions etc.

[BioCam]

ideally this would be named iswap_rotation_drive_request_predefined_positions etc.

very good point, will update immediately

[BioCam]

implemented in #1017