Add glTF sampler filters and wrap modes enums

[matthew-rister]

Problem

cgltf_sampler defines filter and wrap modes using cgltf_int, which requires referencing the glTF specification to interpret those integers.

Solution

To resolve this, enumerations representing valid glTF sampler filter and wrap modes are introduced. For backward compatibility, these enumerations retain their original integer values to allow implicit conversion to cgltf_int.

Testing

Project tests were run using tests/test_all.py on Windows (MSVC 19.41.34123) and Ubuntu (GCC 13.2) which passed without any errors. Additionally, these changes were validated on a sample Vulkan glTF loading implementation in C++ as demonstrated by this commit.

Notes

• cgltf_sampler_filter_type was considered, but the convention to prefix enumeration values with their respective type name resulted in excessively verbose names such as cgltf_sampler_filter_type_nearest_mipmap_nearest.
• cgltf_wrap_mode omits the suffix _type because there is precedent with a similar enum: cgltf_alpha_mode.

Closes #256

[zeux]

fwiw I've tested this in gltfpack and it works correctly (no app code changes required). It would probably be more consistent with the rest of the code to omit the _default enum value for wrap mode (and just use _repeat explicitly) but it works either way.