fix: Texture2D without image data and streamed Texture2DArray

[nichinichisou0609]

Two fixes for reading texture data; one commit each, and each commit adds a regression test that fails on its parent and passes with the fix.

• Textures without size or stream data. A dynamic font keeps its glyph texture in a Texture2D named "Font Texture" with a width and height of 0 and no image data. Like every texture that is not streamed, it serializes m_StreamData with an empty path, offset 0 and size 0. Texture2D.get_image_data looked up a resource whenever m_StreamData was set, so reading .image of such a texture passed an empty name to get_resource_data, which opened the environment directory as a file and failed with PermissionError on Windows and IsADirectoryError on Linux. A texture with a size and no image data took the same path. get_image_from_texture2d now returns an empty image for a texture without width or height, as parse_image_data already does, without fetching any data, and get_image_data reads a resource only when m_StreamData.path names one and raises ValueError("No image data found") otherwise.
• Streamed Texture2DArray. Texture2DArray.images read m_StreamData only when image_data was None. A streamed array serializes image_data as an empty byte string, so every streamed array failed with Texture2D has no image data. Texture2DArray now has get_image_data() with the same rules as Texture2D.get_image_data(), and images decodes the layers with the platform of the object reader instead of platform 0, as Texture2D does.

tests/test_texture.py (new) builds the objects in memory: a 0x0 texture and a 2x2 texture without data, both without loading any dependency, and a two-layer RGBA32 array stored inline, stored in a .resS registered with Environment.register_cab, and without data. The inline array passes before the change as well and is there as a baseline.

Validation on Windows x86_64, CPython 3.11.13, pytest 9.1.1, Pillow 12.3.0. The compiled path uses the UnityPyBoost extension of the 1.25.4 wheel; UnityPyBoost/ has no changes between 1.25.4 and 417d595. A "Font Texture" from a player build made with Unity 6000.3 raised PermissionError before the change and returns a 0x0 image after it.

Check	Result
New tests against unmodified 417d595	4 failed, 1 passed (the inline array baseline)
Each commit's tests against its parent commit	fail before, pass after, with and without the extension
Complete suite, with / without the extension	53 passed / 53 passed
ruff check and ruff format --check	Passed

python -m pytest -q tests/test_texture.py
python -m pytest -q tests