Add datetime/timedelta support to pytest.approx (#8395)

[hamza-mobeen]

Closes #8395

Description

This PR introduces native support for comparing datetime.datetime and datetime.timedelta objects using pytest.approx().
Following the guidelines discussed in #8395:

• An explicit absolute tolerance (abs) must be provided as a datetime.timedelta object. We intentionally avoid providing default tolerances as time comparisons lack sane defaults.
• Relative tolerances (rel) are not supported for time comparisons and will raise a TypeError with an informative message.
• nan_ok is also explicitly rejected for time comparisons.
• Implemented ApproxTimedelta as an internal helper class to manage this specific comparison logic.
• Included test coverage in testing/python/approx.py ensuring there are no regressions with existing numeric approximation behavior.

Usage Example

>>> from datetime import datetime, timedelta
>>> dt1 = datetime(2024, 1, 1, 12, 0, 0)
>>> dt2 = datetime(2024, 1, 1, 12, 0, 0, 500000)
>>> dt1 == approx(dt2, abs=timedelta(seconds=1))
True

Example Test Coverage

class TestApproxDatetime:
    # ...
    def test_datetime_error_message(self):
        from datetime import datetime, timedelta
        dt1 = datetime(2024, 1, 1, 12, 0, 0)
        dt2 = datetime(2024, 1, 1, 12, 0, 5)  # 5 seconds off
        with pytest.raises(AssertionError, match="comparison failed"):
            assert dt1 == approx(dt2, abs=timedelta(seconds=1))
    def test_rejects_rel(self):
        from datetime import datetime, timedelta
        with pytest.raises(TypeError, match="does not support relative tolerance"):
            approx(datetime(2024, 1, 1), rel=0.1, abs=timedelta(seconds=1))
    # ... (21 tests in total)

Checklist

• Include documentation when adding new features.
• Include new tests or update existing tests when applicable.
• Allow maintainers to push and squash when merging my commits. Please uncheck this if you prefer to squash the commits yourself.
• Add text like closes #XYZW to the PR description and/or commits (where XYZW is the issue number).
• If AI agents were used, they are credited in Co-authored-by commit trailers.
• Create a new changelog file in the changelog directory, with a name like <ISSUE NUMBER>.<TYPE>.rst.
• Add yourself to AUTHORS in alphabetical order.

[hamza-mobeen]

Hi @RonnyPfannschmidt ,
This PR is ready for review. Please I would like you take a look when you have a moment, and let me know if you have any feedback or if further adjustments are needed.
Thanks!

[RonnyPfannschmidt]

At first glance this looks good

Im currently a bit stretched and hope to take a closer look next week

[hamza-mobeen]

At first glance this looks good

Im currently a bit stretched and hope to take a closer look next week

no problem thanks.

[hamza-mobeen]

Hello @RonnyPfannschmidt I'm still waiting for your feedback. thanks

[RonnyPfannschmidt]

overall this looks good

please check whats implemented in the base classes
please review our ai guidelines - i believe you are missing a few co-authored headers

[RonnyPfannschmidt]

this and a few more methods here seem to be copies from the base class

[hamza-mobeen]

@RonnyPfannschmidt I've made an update to this please check it out when you free