Add NumPy upper-bound pin for Python 3.14 compatibility

[FaryalRizwaan]

This PR adds a Python 3.14–specific NumPy version constraint in pyproject.toml to fix dependency resolution failures when installing opencv-python on Python 3.14.

Issue: #1165 – Installation fails on Python 3.14 because no compatible NumPy version is selected during build dependency resolution.

Changes

Added an environment marker in pyproject.toml to require numpy>=2.1.3,<2.2 for python_version >= '3.14'.

Preserves existing dependency behavior for Python 3.8–3.13.

No changes to setup.py; the fix is fully compliant with PEP 518 and modern packaging standards.

Testing

Verified dependency resolution using pip install --dry-run -e ..

Confirmed that the new marker does not affect installation on supported Python versions (3.8–3.13).

The pinned NumPy version (2.1.3) is published on PyPI and declares Python 3.14 support via classifiers.

This minimal, forward-compatible change ensures opencv-python remains installable as Python 3.14 adoption begins.

[ayushrajput6128]

This PR correctly adds a Python 3.14–specific NumPy constraint and resolves the missing dependency case described in #1165.
The environment marker is forward-compatible and preserves existing behavior for Python 3.8–3.13.
Looks good to me.

[FaryalRizwaan]

Thanks for the review, @ayushrajput6128 ! Glad to hear the environment markers look correct to you.

[mhicks-cfs]

Versions should not be overly constrained, please see #1140

[lucalista]

Release 4.13.0.90, which supports Python 3.14, is not yet in PyPI. Is there any scheduled date for releasing it under PyPI?

[rgommers]

This PR is definitely incorrect. Note that exact pins for numpy are no longer needed since numpy 1.25.0 (see https://numpy.org/devdocs/release/1.25.0-notes.html#compiling-against-the-numpy-c-api-is-now-backwards-compatible-by-default).

A more reasonable change, which would be an actual improvement, would be to change "==2.1.3"to">=2.1.3"`.

[rgommers]

And that approach was already taken in gh-1121 (still open), so I'd just close this PR.