Create tests

[edoyango]

Probably starting with API tests - to avoid mistakes like in (WEHI-ResearchComputing/DynamicDet#4)

[MihinP]

Add unit tests for CLI commands and core functionality

Problem
PartiNet currently lacks unit tests, leading to:

• Broken commits/merges that go undetected
• Regression errors during development
• Difficulty verifying that commands work correctly after changes
• No automated validation in CI/CD pipeline

Examples
WEHI-ResearchComputing/DynamicDet#4
#31
#35

Proposed Solution
Implement a unit test suite covering:

• CLI commands: Test all command-line entry points and argument parsing
• Core functions: Model loading, weight downloading, coordinate output
• Data processing: Micrograph loading, preprocessing, denoising pipeline
• File I/O: Reading/writing coordinates, handling different formats
• Error handling: Invalid inputs, missing files, corrupted data