GH-47686: [Docs][Python] Split the Python Parquet docs into separate items

[AlenkaF]

Rationale for this change

The current parquet section is one-page and covering lots of topics. As per #46601 the parquet section is most visited and would therefore need a bit of maintenance/content update.

What changes are included in this PR?

• Parquet documentation is split in 4 different subpages (index.rst, parquet.rst, parquet_datasets.rst and parquet_encryption.rst).
• Some additional content is added

Are these changes tested?

Via the docs preview

Are there any user-facing changes?

No

• GitHub Issue: [Docs][Python] Split the Python Parquet docs into separate items #47686

[AlenkaF]

@github-actions crossbow submit preview-docs

[github-actions]

Revision: 156850c

Submitted crossbow builds: ursacomputing/crossbow @ actions-937dad9db2

Task	Status
preview-docs

[AlenkaF]

I have used Claude for suggesting the split of pyarrow parquet page and to look through the code and the git log history for any features/changes that might be missing from the docs. From what was suggested I continued with the work on my own.

I have split the changes in different commits so the change will be easier to review (due to the docs split, the change is bigger than it really is).

commit 1: restructure of the content, no content changes @thisisnic, do you mind having a look?
commit 2: add content about filtering and ability to write bloom filters @mapleFU, do you mind having a look?
commit 3: add section on iter_batches @raulcd, do you mind having a look?
commit 4: add section on binary/list_type option on read, reading extension types @pitrou @paleolimbot, do you mind having a look?
commit 5: datasets note on single file partitions not being included
commit 6: update parquet writer's parameter list @raulcd, do you mind having a look?
commit 7: update encryption section adding info on key rotation and direct encryption @adamreeve, do you mind having a look?

Rendered docs are available here: https://s3.amazonaws.com/arrow-data/pr_docs/50419/python/parquet/index.html

[Copilot]

Pull request overview

Splits the PyArrow Parquet user-guide documentation into multiple focused pages to improve navigability and enable incremental maintenance, aligning with the broader Python docs revision effort.

Changes:

• Replaces the single large Parquet guide page with a section index plus dedicated subpages (single-file IO, datasets, type handling, encryption).
• Updates the Python docs toctree to point at the new Parquet section entry point.
• Adds/relocates some additional Parquet-related content during the split (e.g., content-defined chunking).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
docs/source/python/parquet/parquet.rst	New “single files” Parquet IO page (read/write, metadata, filtering, etc.).
docs/source/python/parquet/parquet_type_handling.rst	New page for Parquet read/write type-handling options.
docs/source/python/parquet/parquet_datasets.rst	New page for partitioned datasets / multi-file Parquet usage.
docs/source/python/parquet/parquet_encryption.rst	New page for Parquet modular encryption docs.
docs/source/python/parquet/index.rst	New Parquet section landing page with toctrees to subpages.
docs/source/python/parquet.rst	Removes the previous monolithic Parquet documentation page.
docs/source/python/index.rst	Updates the Python guide toctree to reference the new Parquet section entry.