Add AMDGPU CI and support AMDGPU through KernelAbstractions

[vchuravy]

• Add CI for AMDGPU.jl
• add extension for AMDGPU
• fixup! add extension for AMDGPU

Partially co-written by Claude Code.

Sibling to #2833 and child PR to #2590

TODO

• Prefer aligned_sizeof JuliaGPU/AMDGPU.jl#887
• Support Symbols on the GPU JuliaGPU/AMDGPU.jl#888
• Add AMDGPU.jl extension JuliaArrays/ArrayInterface.jl#479

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.07%. Comparing base (4c42b01) to head (67d27de).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ext/TrixiAMDGPUExt.jl	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2834      +/-   ##
==========================================
- Coverage   97.09%   97.07%   -0.02%     
==========================================
  Files         609      610       +1     
  Lines       47493    47501       +8     
==========================================
  Hits        46111    46111              
- Misses       1382     1390       +8     

Flag	Coverage Δ
unittests	97.07% <0.00%> (-0.02%)	⬇️

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[benegee]

LGTM

[ranocha]

Could you please adapt the compat bounds to fix Downgrade CI?

[sloede]

LGTM - thanks! I'd also like to have @ranocha take a quick look before merging this

[ranocha]

Thanks! I just have a minor comment.

[ranocha]

Can you please fix the buildkite CI job?

[benegee]

Let's try again, with #2904 merged.

[ranocha]

Thanks