Support multi-threaded writing of Parquet files with modular encryption

[rok]

Closes #7359.

Rationale for this change

This is to enable concurrent column writing with encryption downstream (e.g. with datafusion). See #7359 for more.
See https://github.com/apache/arrow-rs/pull/7111/files#r2015196618

What changes are included in this PR?

• ArrowRowGroupWriterFactory.create_row_group_writer now passes a FileEncryptor to ArrowColumnWriterFactory that can later be used to write columns concurrently.
• Several methods and properties are now pub.
• Minor change to how encryption tests read test data.

Are these changes tested?

Yes.

Are there any user-facing changes?

ArrowRowGroupWriterFactory, ArrowRowGroupWriter, ArrowRowGroupWriterFactory::new, ArrowRowGroupWriterFactory.create_row_group_writer , .. are now pub. Shouldn't be breaking but perhaps needs review.

[adamreeve]

👍 I like the approach of exposing the ArrowRowGroupWriterFactory to handle passing through the file encryption properties. We should probably also update the documentation on ArrowColumnWriter to encourage users to use this API, and/or add documentation to get_column_writers to encourage users to use this approach for compatibility with encryption.

There seem to be a lot of extra things that have been exposed publicly in this PR that don't need to be though, which makes it hard to follow what changes are actually needed. We should minimize how much is public so it's easier for users to follow documentation and see which APIs they should be using, and so that internal details can be changed later.

[rok]

Thanks for the quick review @adamreeve !
I've moved schemas and writer properties to ArrowRowGroupWriterFactory as you suggested.
Test also now uses tokio channels.