Add env variables to configure manifest cache

[kris-gaudel]

Closes #2952

Rationale for this change

Through discussion in issue #2325, we realized that there was a memory leak in the manifest cache. PR #2951 fixed this memory leak, but we decided that it would be best for developer experience if we developers could configure the cache for their needs.

This includes the ability to disable/enable the manifest cache, and configure its size

Are these changes tested?

Yes - unit tests are included to verify these changes

Are there any user-facing changes?

Yes:

• PYICEBERG_MANIFEST__CACHE__ENABLED can be used to enable/disable the cache, and
• PYICEBERG_MANIFEST__CACHE__SIZE can be used to configure the size of the manifest cache

[kris-gaudel]

@kevinjqliu @Fokko @rambleraptor Please lmk what you think!

[thomas-pfeiffer]

@kris-gaudel I have a few questions:

• Would it make sense to list the new configuration parameters somewhere in mkdocs/docs/configuration.md, so that it shows up in the documentation as well?
• Would it make sense to allow PYICEBERG_MANIFEST__CACHE__SIZE to be set to 0 to effectively disable the cache?
  • It's mentioned in Deprecate support for cache(self) returning None. Why? tkem/cachetools#352 (comment) that maxsize = 0 can be used to bypass the cache.
  • This would make PYICEBERG_MANIFEST__CACHE__ENABLED obsolete, right?
• What's the added benefit of having a _ManifestCacheManager class?
  • Wouldn't _manifest_cache: LRUCache[str, ManifestFile] = LRUCache(maxsize=int(environ.get("PYICEBERG_MANIFEST__CACHE__SIZE", 128))) do the trick as well? (obviously an oversimplified example)

[Fokko]

Thanks @kris-gaudel for raising this. I think it is reasonable to make this configurable. But I think we should reduce the number of changes and simplify where possible. For example, do we need PYICEBERG_MANIFEST__CACHE__ENABLED or can we set PYICEBERG_MANIFEST__CACHE__SIZE to 0 instead.

[geruh]

nit: do we need this variable here, adds a bit of noise with the change

[geruh]

Depending on the init functionality. We can probably remove the clear since it's a no-op after calling your current init function.

[geruh]

I think we can still simplify this to:

_manifest_cache_size = Config().get_int("manifest-cache-size") or _DEFAULT_MANIFEST_CACHE_SIZE
_manifest_cache: LRUCache[str, ManifestFile] = LRUCache(maxsize=_manifest_cache_size)

It someone really wants to disable caching. All I gotta do is just set this value to something like 1. The overhead here is pretty negligible. Unless there is a strong opinion for a case in which we never allocate a lrucache instance...