feat(parquet): add StatisticsConverter::from_column_index

[kumarUjjawal]

Which issue does this PR close?

• Closes StatisticsConverter does not support nested fields (e.g. struct fields) #9539.

Rationale for this change

StatisticsConverter::try_new resolves columns through parquet_column(), which only supports top-level non-nested columns. Because of that, callers that already know the Parquet leaf index for a nested field cannot use StatisticsConverter to read statistics for that field.

This blocks reading stats for fields inside structs.

What changes are included in this PR?

• add StatisticsConverter::from_column_index(...)
• keep StatisticsConverter::try_new(...) behavior unchanged
• update docs to explain when to use each constructor
• add a test that writes a struct column and reads statistics for each child
  field through the new API

Are these changes tested?

Yes

Are there any user-facing changes?

Yes.

This adds a new public constructor: StatisticsConverter::from_column_index(...)

There are no breaking changes.

[adriangb]

I think @friendlymatthew is also working on this, maybe you can coordinate efforts?

[alamb]

There is this one from @friendlymatthew

• introduce StatisticsConverter::from_column_index #9540

it would be super helpful to combine efforts (e.g. by reviewing the PRs together) and pinging me when you think they are ready

[kumarUjjawal]

I have reached out to @friendlymatthew for this, I will get back to you once we decide how to proceed forward.