Modernize core modules: pathlib, type hints, DRY engine consolidation

[Copilot]

Modernize and simplify the Mesofield framework across core modules, reducing ~68 net lines while fixing several pre-existing bugs that prevented tests from running.

Modernization

• config.py — pathlib.Path: Replace all os.path usage with pathlib.Path for BIDS path generation, hardware resolution, and JSON persistence. _save_dir is now a Path internally.

• engines.py — DRY consolidation: DevEngine now inherits from PupilEngine instead of duplicating the entire exec_sequenced_event loop (~60 lines removed). Only overrides set_config/setup_sequence/teardown_sequence to skip NIDAQ behavior.

• Type hints (8 files): from __future__ import annotations + modern union syntax (str | None, list[str], dict[str, Any]) across __init__, __main__, base, config, hardware, protocols.

• __init__.py: Added __all__ for explicit public API.

Bug fixes

• base.py: Hardcoded cameras[1]/cameras[0] → safe iteration. Previously crashed with fewer than 2 cameras.
• data/writer.py: Removed circular import of BASE_DIR from crop_enhance_mp4 (already defined locally) that caused cv2 import failure at module load.
• __main__.py: Removed hardcoded D:\jgronemeyer\... Windows path in plot_session.
• test_workflow.py: Fixed indentation error, invalid YAML, reference to non-existent DataSaver.writer_for, missing data.setup() call.

Example: config path handling before/after

# Before
bids = os.path.join(f"sub-{self.subject}", f"ses-{self.session}")
return os.path.abspath(os.path.join(self.save_dir, bids))

# After
return str(Path(self.save_dir) / f"sub-{self.subject}" / f"ses-{self.session}")

# Before: DevEngine duplicated ~60 lines from PupilEngine
class DevEngine(MDAEngine):
    def exec_sequenced_event(self, event): ...  # identical copy

# After
class DevEngine(PupilEngine):
    def set_config(self, cfg):
        self._config = cfg
        self.nidaq = None  # skip NIDAQ

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