Update SGP and samples to use new SGL views API

[Hymenium]

Following #52 and #50, this PR updates sokol_gp to the latest sokol headers and migrates image usage to the new views API with minimal changes.

What's changed:

• Sokol headers (/thirdparty/) : Updated to current Sokol master (floooh/sokol@8c06b5e) .
• Images -> Views: API now expects texture views instead of raw images. As before, views (and images) must be managed by the caller. Checks and asserts follow the current style.
• Helper: Added sgp_make_texture_view_from_image() to create a simple 2D texture view from an image.
• Sizing: View size is computed using the view (mip base considered for future-proofing).
• Internals: Using public sokol functions for image size, but the previous _sg_lookup_image path is left in comments for reference.
• Samples: Updated samples that used images to use views. Everything tested compiles and seem to run as expected on Windows (11) using GLCORE or D3D11 (HTML sample not tested).

Breaking changes:

• Functions that previous took sg_image now expect sg_view.
• For covenience: sg_view v = sgp_make_texture_view_from_image(img, label); and v can be passed to the new API.

Rationale:
Aligns sokol_gp with the new views API, without taking on managing the views internally.

Testing:

• Platform: Windows 11
• Backends: GLCORE, D3D11
• Status: All samples run as expected (except sample-shell.html not tested).

Documentation:
Not updated in this PR. Migration is straightforward (replace images with views), and the new helper can be recommend for most existing workflows

Migration example:
Before:
sg_image img = ...;
sgp_set_image(ch, image);

After:
sg_image img = ...;
sg_view view = sgp_make_texture_view_from_image(img, "label");
sgp_set_view(ch, view);

[Hymenium]

This PR should solve the issues in #51 and #53.