MINOR: [Docs] Mention validate() helpers in Python IPC docs

[shashbha14]

This PR adds a short “Security considerations for untrusted IPC data” section
to the Python IPC docs. It:

• Explains that you should explicitly validate RecordBatches/Tables when
  reading IPC data from untrusted or semi‑trusted sources.
• Points to RecordBatch.validate() and Table.validate() as the relevant
  validation helpers.
• Shows small code snippets using these methods with pa.ipc.open_stream
  and pa.ipc.open_file.

It doesn’t try to answer the broader questions in #49241 (updates to
format/Security.rst or adding an always_validate option), but it should
still make the validation APIs more discoverable for PyArrow users.

[github-actions]

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[raulcd]

I am unsure this really tackles the issue that was raised. The issue has two parts one about the new security guidelines:
https://github.com/apache/arrow/blob/68d13685b4e3914ff2b36eeca606ae428b8e3485/docs/source/format/Security.rst
and two a question on whether a new flag on the IPCReadOptions like always_validate makes sense or not.
This PR is not tackling any of those concerns.

[shashbha14]

Thanks for the review and clarification.You’re right, this PR doesn’t address the Security.rst text or the
always_validate flag question. I’ve updated the title/description so this
is just a small Python IPC docs improvement instead of trying to close
#49241. I’m happy to leave the main issue open for the broader discussion and any
changes you’d like to make on the Security page itself.