Migrate setup.py to pyproject.toml and add pixi configuration

[tfehlmann]

Summary

• Migrate packaging from imperative setup.py to declarative PEP 621 metadata in pyproject.toml
• Add pixi configuration for automatic binary dependency management via conda-forge
• Delete setup.py

Details

pyproject.toml migration

All setup() arguments are converted to their PEP 621 equivalents:

• Build system: setuptools>=68.0 with setuptools.build_meta backend
• Project metadata: name, description, readme, license, Python version requirement
• Dynamic version: read from pylabrobot/version.txt via [tool.setuptools.dynamic]
• Dependencies: all install_requires and extras_require groups preserved with identical pins
• Entry points: lh-server and plr-gui console scripts
• Package discovery: namespaces = false to match find_packages() behavior exactly
• Package data: visualizer/* and version.txt unchanged

Existing [tool.ruff] configuration is preserved.

Pixi configuration

Adds [tool.pixi.*] sections for automatic binary dependency management:

Feature	Conda Package	Purpose
fw	libusb	USB device communication
plate-reading	libftdi	FTDI device communication
inheco	libhidapi	HID device communication
dev	all of the above	Development environment

Each feature environment includes editable PyPI installation with the corresponding extras.

Pixi tasks mirror the Makefile: test, lint, format, format-check, typecheck.

Users who do not use pixi are completely unaffected — pip install works identically.

Verification

• pip install -e '.[dev]' succeeds
• python -m build produces valid wheel and sdist
• Wheel file list is identical to the previous setup.py build (verified via diff)
• python -c "from pylabrobot import __version__" returns 0.1.6
• Entry points (lh-server, plr-gui) resolve correctly
• All 821 tests pass via both python -m pytest and pixi run -e dev test
• No CI workflow changes required

Test plan

• pip install -e '.[dev]' works
• python -m build produces valid artifacts
• All tests pass
• Entry points resolve
• CI passes without changes

[rickwierenga]

do we need this?

[tfehlmann]

can be dropped, although since you pinned all packages that's just a more precise pinning, but will drop it