tests: Update pygrass doctests for NumPy 2 compatibility (#4100)

[Khansa435]

Description

Fixes #4100
(and also addresses the underlying cause behind #4116 )

This PR updates the gunittest doctest suite to be fully compatible with NumPy 2.0+.

NumPy 2.0 introduced changes to the string representation of arrays and scalar types (e.g., scalars now print as np.int32(1) instead of 1, and arrays with non-default dtypes are formatted differently depending on the default platform size). This caused several doctests to fail, leading to test_pygrass_raster_doctests.py being excluded from the test suite.

As discussed with @echoix in the issue thread, since main is moving towards the 8.6 release, the strategy here is to explicitly target the NumPy 2 string representations natively rather than retaining backward compatibility with NumPy 1.x string outputs.

Changes Made

• Bumped CI requirements: Updated numpy to numpy>=2.0.0 in .github/workflows/python_requirements.txt to guarantee the test environments use NumPy 2.
• Un-excluded raster doctests: Re-enabled python/grass/pygrass/raster/testsuite/test_pygrass_raster_doctests.py in .gunittest.cfg so the test suite will run these tests again.
• Updated scalar representations: Fixed the expected output in python/grass/pygrass/utils.py (get_raster_for_points) to expect the explicit np.int32(1) NumPy 2 scalar wrapper.
• Updated array representations: Removed the dtype= parameter from expected Buffer outputs in python/grass/pygrass/raster/init.py. In NumPy 2 on standard configurations, these standard buffer arrays omit the dtype parameter string during formatting.

[Khansa435]

Hi @echoix @wenzeslaus ! I've updated this PR with a fix for NumPy 2.x compatibility using # doctest: +ELLIPSIS wildcards.

This approach supports both NumPy 2 and the older NumPy 1.x used in the Ubuntu CI. Could you please approve the workflows to run as they require approval from a maintainer? :)

[Khansa435]

@echoix @wenzeslaus @ninsbl
Can you please take a look and review the changes I made :)

[Khansa435]

Hi @echoix @wenzeslaus @ninsbl
Just a polite followup on requesting for the review of my code changes please :)