docs: explain comparison and sorting of Arrow objects

[x0Lazarus]

Description of Changes

The guide does not explain that Arrow objects support equality, ordering and sorting, leaving their timezone behavior unclear. Add a Compare section after Properties, as suggested in #981.

The examples show equal instants with different offsets, sorting, and comparisons with datetime objects. The text explains that Arrow follows Python's datetime rules, including the repeated-hour case where comparing local times ignores fold. A short example shows how converting to UTC distinguishes those instants.

Validation on Windows with Python 3.12: all 14 new example statements pass doctest; the full suite passes with 1,901 tests and one existing platform skip; all configured pre-commit hooks pass; doc8 and the Sphinx HTML build with warnings treated as errors pass. Other Python versions and operating systems were not tested locally. No library code changes.

Closes #981.

Pull Request Checklist

• Added tests for changed code. Not applicable: documentation only; the new examples were executed with doctest.
• All tests pass when run locally, with the existing Windows negative-timestamp skip noted above.
• All linting checks pass when run locally.
• Updated documentation.
• Code is up-to-date with the master branch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (2224255) to head (db7031a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Hits          2315      2315           

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