Add NanoXRP board support + XRPLib 2.3.0

[SaintSampo]

Add NanoXRP board support + XRPLib 2.3.0

Summary

Adds the NanoXRP board to the firmware repo and introduces XRPLib 2.3.0, a
new library release that combines the NanoXRP support from the upstream
XRP_MicroPython main branch with the dashboard/puppet stack already shipping
in 2.2.1. The three MicroPython board projects are repointed at the new release.

What's included

1. NanoXRP board

• boards/xrp-nano/ — MicroPython 1.28.0 firmware (firmware.uf2 + registry),
  board selector (boards/xrp-nano.json), and a micropython project.

2. XRPLib 2.3.0 (boards/XRPLib/2.3.0/)

Built from the 2.2.1 release as a base, then the NanoXRP + buzzer work was
layered on top. Net result vs 2.2.1:

Kept from 2.2.1 (unchanged): dashboard.py, puppet.py, the puppet/XPP-based
gamepad.py, ble/, phew/, and all shared modules/examples.

Brought in from XRP_MicroPython@main (NanoXRP support):
board.py, motor.py, imu.py, encoder.py, encoded_motor.py,
reflectance.py, differential_drive.py, defaults.py, plus new
XRPLib/buzzer.py and XRPExamples/buzzer_examples.py. This adds NanoXRP board
detection (motor direction, IMU axis remap, encoder gear ratio, wheel geometry
and per-board PID gains), a buzzer module, a middle reflectance sensor, and
board-attribute-gated 4th motor / 4 servos — all guarded so existing Beta/2350
boards are unaffected.

Hand-merged: resetbot.py — union of both lineages (keeps 2.2.1's
reset_dashboard, adds the buzzer reset and board-attribute-driven motor/servo
handling).

3. Gamepad architecture decision

The two source lineages had incompatible gamepad implementations (upstream
main: BLE UART; 2.2.1: puppet/XPP). 2.3.0 keeps the puppet-based gamepad so
the dashboard continues to work. The upstream BLE gamepad path is intentionally
not carried over.

Bug fixes (folded into 2.3.0)

Three pre-existing defects in upstream main were fixed while importing the code.
All three still exist upstream and should be fixed there too:

1. differential_drive.py — track_width never assigned. The "centralize
   defaults" refactor assigned self.wheel_track but the turn/heading math reads
   self.track_width, which was never set → AttributeError on encoder-based
   (no-IMU) straight()/turn(). Standardized on self.track_width.
2. differential_drive.py — explicit wheel args dropped. wheel_diam/
   wheel_track were only assigned inside the == 0.0 sentinel branch, so passing
   an explicit non-zero value left the attribute unset → AttributeError. Added
   else branches so explicit values are honored and 0.0 still means auto-detect.
3. encoded_motor.py — speed PID not reset on set_speed(). The persistent
   speed controller kept stale integral windup and a frozen prev_time across
   stop→restart, causing an effort kick / timestep spike on the first update after
   restart. set_speed() now calls clear_history() when starting control.

Project version references

Project	xrplib before	xrplib after
xrp-nano / micropython	(new)	xrplib-2.3.0
xrp-beta / micropython	xrplib-2.2.1	xrplib-2.3.0
xrp-2350 / micropython	xrplib-2.2.1	xrplib-2.3.0
xrp-2350 / sparkfun-red-vision	xrplib-2.2.1	xrplib-2.2.1 (unchanged)
xrp-2350 / agxrp	xrplib-2.1.3	xrplib-2.1.3 (unchanged)

xrplib-2.3.0 is registered as the newest entry in boards/XRPLib/index.json.

Generation & verification

• files.json regenerated with the standard gen-firmware-manifests.mjs logic
  (verified byte-for-byte against the tool's output); xrplib.zip LSP stub bundle
  rebuilt to include buzzer.py and the fixes.
• All XRPLib modules syntax-compile; JSON manifests validate; line endings kept
  CRLF-consistent with the rest of the repo.