Make ParquetField public

[XiangpengHao]

Which issue does this PR close?

Closes #.

Rationale for this change

ParquetField (and its friends) are foundation types in the crate, without this being public, many of the functions can't be called, e.g., build_array_reader. If this is public, downstream users can easily hooking their own parquet reading logic while still reusing much of the existing code.

What changes are included in this PR?

Are there any user-facing changes?

[alamb]

Sounds good to me

[etseidl]

Seems reasonable to me too.

[tustvold]

ParquetField currently has public members, we might want to change this. As it stands even adding a field would be a breaking API change once made public

Taking a step back, why do you want this public, what public APIs make use of it? build_array_reader is not public, or at least shouldn't be...

[XiangpengHao]

build_array_reader is not public, or at least shouldn't be...

build_array_reader is public under experimental feature.

why do you want this public

The current ParquetRecordBatchReader is a black box, my use case would want finer control over how data is read, e.g., decode timing.

As it stands even adding a field would be a breaking API change once made public

That's a good point, but this specific type has not changed for 3 years and probably won't change for a while.

[tustvold]

build_array_reader is public under experimental feature.

Perhaps we could make this public under the same experimental feature gate? I'm being cautious as we've been stung in the past by exposing too much of this crates' internals

[XiangpengHao]

Perhaps we could make this public under the same experimental feature gate?

Sounds great! Will do soon

[alamb]

Marking as draft -- please mark it as ready to review when it is

[XiangpengHao]

I'll need to think more carefully on what should be public, let's close this until I have a better understanding of how to proceed. Thank you for the review! @alamb @etseidl @tustvold