This updates the pathlib.PurePath.with_segments() documentation to describe
the Python 3.14 behavior added in gh-128520 / GH-130199.

Some pathlib methods now use the presence of a with_segments attribute to
decide whether an argument is already a path object. If the attribute is
present, the argument is used directly; otherwise, it is converted through
with_segments(). This is relevant for authors of pathlib subclasses and
third-party path-like/path-adjacent objects.

Validation:

• git diff --check
• env PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1 make -C Doc check
• make -C Doc html SPHINXOPTS='-W --keep-going -q'

Notes:

• No NEWS entry is included because this is a documentation-only change.
• Running make -C Doc check without PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1
  failed while building a pre-commit dependency (regress) because PyO3 0.26.0
  does not yet recognize Python 3.15.

• Issue: Document pathlib with_segments duck typing for path object arguments #153390