feat: add dispensing module with Formulatrix Mantis backend

[xbtu2]

Summary

Adds a new pylabrobot/dispensing/ module for chip-based contactless liquid dispensers, following PLR's Machine/Backend architecture pattern. The Formulatrix Mantis is the first backend implementation.

New Module Structure

pylabrobot/dispensing/
├── __init__.py                    # Exports: Dispenser, DispenserBackend, DispenseOp
├── backend.py                     # ABC: DispenserBackend
├── standard.py                    # Dataclass: DispenseOp
├── dispenser.py                   # Front-end: Dispenser(Machine)
├── chatterbox.py                  # ChatterboxBackend for testing
├── dispenser_tests.py             # Front-end unit tests (6 tests)
└── mantis/
    ├── __init__.py                # Exports: MantisBackend
    ├── mantis_backend.py          # MantisBackend(DispenserBackend)
    ├── fmlx_driver.py             # Low-level FMLX protocol driver
    ├── mantis_kinematics.py       # Kinematics + map generator
    ├── mantis_constants.py        # Constants, chip paths, PPI sequences
    ├── mantis_sequence_parser.py  # Sequence file parser
    └── mantis_tests.py            # Mantis-specific unit tests (22 tests)

Design Highlights

• Dispenser(Machine) front-end with @need_setup_finished decorator
• DispenserBackend ABC with setup(), stop(), dispense(ops) interface
• DispenseOp frozen dataclass (resource, volume, chip)
• MantisBackend — full init sequence, chip lifecycle (attach/prime/dispense/detach), pressure control
• FmlxDriver — accepts PLR's pylabrobot.io.ftdi.FTDI via dependency injection
• Proper enums — MotorStatusCode(IntFlag) with error_mask(), PEP 8 naming
• Configurable chip_type_map per instrument instance
• 28 unit tests all passing
• Chatterbox backend for device-free testing

Usage Example

from pylabrobot.dispensing import Dispenser
from pylabrobot.dispensing.mantis import MantisBackend

d = Dispenser(backend=MantisBackend(
    serial_number="M-000438",
    chip_type_map={3: "high_volume", 4: "high_volume", 5: "low_volume"},
))
await d.setup()
await d.dispense(plate["A1:H12"], volume=5.0, chip=3)
await d.stop()

Testing

28 passed in 0.14s

All pre-commit hooks pass (ruff format, ruff check, typos).

[rickwierenga]

sweet! thanks for the PR!

mind if I rebase this onto the v1b1 architecture?