Fix Pillow 12.2 encoder compatibility in pil_to_numpy

[aswanth-07]

Summary

• Pass explicit image extents to Pillow's raw encoder, which is accepted by older supported releases and required by Pillow 12.2.
• Add regression coverage for writable grayscale and RGB arrays.

Fixes #3782

Validation

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 py -3.13 -m pytest -o addopts='' tests/utils/test_data_utils.py -q (2 passed with Pillow 11.0.0)
• Direct pil_to_numpy checks passed for grayscale and RGB images with Pillow 12.2.0.
• py -3.13 -m ruff check nerfstudio/data/utils/data_utils.py tests/utils/test_data_utils.py (passed)
• py -3.13 -m ruff format --check nerfstudio/data/utils/data_utils.py tests/utils/test_data_utils.py (passed)
• git diff --check (passed)
• The exact pristine upstream commit fails under Pillow 12.2.0 with TypeError: function takes exactly 2 arguments (1 given).

AI assistance disclosure: AI-assisted development tools were used during investigation and implementation. The reported tests were run against the final diff.