fix: Ensure the CachedParquetFileReader respects the metadata prefetch hint

[nuno-faria]

Which issue does this PR close?

• Closes CachedParquetFileReader should respect the metadata prefetch hint #17279.

Rationale for this change

Uses the metadata_size_hint when reading metadata in the CachedParquetFileReader, if available, so the behavior is consistent with the documentation.

What changes are included in this PR?

• Added metadata_size_hint to CachedParquetFileReader.

Are these changes tested?

N/A.

Are there any user-facing changes?

No.

[shehabgamin]

Super small PR, looks like this one maybe slipped through the cracks? Probably should make it into DF 50 if possible.
cc @alamb

[alamb]

Thanks @nuno-faria and @shehabgamin

Is there some way we can add a test for this behavior so we don't introduce a regression in the future?

[alamb]

Super small PR, looks like this one maybe slipped through the cracks? Probably should make it into DF 50 if possible. cc @alamb

I think we have already started voting on 50.0.0:

• Release DataFusion 50.0.0 (Aug/Sep 2025) #16799 (comment)

Perhaps you can suggest adding this to the 50.0.0 release on #16799?

[nuno-faria]

Is there some way we can add a test for this behavior so we don't introduce a regression in the future?

I thought about adding one when creating the PR but don't know if the prefetch information is exposed to the outside.