feat: add image download cache

[hollandjg]

This will create an sqlite database cache of all the requests made when downloading images, and allow downloads to be reused across different sessions.

• Add test cases.

[Copilot]

Pull Request Overview

This PR introduces an image download caching mechanism using an SQLite database to cache requests, enabling image downloads to be reused across sessions.

• Added the "requests-cache" dependency in pyproject.toml.
• Extended the load function to optionally use a cached session when a cache directory is provided.
• Updated the CLI in app.py to accept and forward the cache directory parameter.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

File	Description
pyproject.toml	Added requests-cache dependency to manage caching.
src/ebfloeseg/load.py	Added cache_directory parameter and caching session support.
src/ebfloeseg/app.py	Propagated cache_directory parameter to the load function.

Comments suppressed due to low confidence (2)

src/ebfloeseg/load.py:207

• Ensure that requests_cache.CachedSession is being used correctly; it may expect a cache name string rather than a Path object. Consider reviewing the requests-cache documentation to validate the correct parameter type and usage.

        session = requests_cache.CachedSession(cache_directory)

src/ebfloeseg/load.py:166

• Add unit tests to verify the caching functionality when cache_directory is provided and when it is omitted.

    cache_directory: Optional[pathlib.Path] = None,

[cpaniaguam]

I triggered the Copilot review out of curiosity. The changes look good to me but I concur that some tests should be added before merging this feature.