Remove GraphicsAPI generic for WgpuRuntime

[ArthurBrussee]

Checklist

• Confirmed that run-checks all script has been executed.
• Made sure the book is up to date with changes in this PR.

Changes

Slightly cheeky PR so bear with me :)

Ran into some annoying trait bounds while trying to do some stuff and rather than just grumble, felt like I could remove this entirely! A WgpuRuntime is a WgpuRuntime - irregardless of what the graphics API is. This is particularly evident with runtime::init_existing_device() - it's possible to register a DX12 device, and yet run it on a BurnRuntime which just seems wrong!

I understand it's used to manually pick a graphics API, but, you can already do this with

runtime::init_sync<Vulkan>();

This could also be in RuntimeOptions perhaps, for consistency.

All that said, this is a bit of miscellaneous design change in a PR so thanks for bearing with me :)

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.07%. Comparing base (5e58ae1) to head (2922f83).
Report is 4 commits behind head on main.

Files	Patch %	Lines
crates/burn-wgpu/src/runtime.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1888      +/-   ##
==========================================
- Coverage   86.14%   86.07%   -0.07%     
==========================================
  Files         778      781       +3     
  Lines       90827    91615     +788     
==========================================
+ Hits        78245    78862     +617     
- Misses      12582    12753     +171     

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[nathanielsimard]

So if I understand it well, this is where the default runtime is actually created for a device type. It uses the AutoGraphicsApi to select the most appropriate adaptor for the device. If you want to specify manually the graphics API for a device type, you have to use init_sync or init_async!

I don't think this is a bad thing, now the WgpuBackend only has typical backend generics, and runtime options can be changed using the init functions! Before merging I would add a bit more documentation on the WgpuRuntime and WgpuBackend pointing to the right direction to specify backend and runtime options.

[ArthurBrussee]

Yep that's right! Seemed coherent to me to have one "advanced initialize" place, glad you agree :)

Have added some docs now, and a random code cleanup, lmk how this looks!