Failures in `webgpu:api,operation,rendering,3d_texture_slices:*`

[andyleiserson]

These tests were passing and started failing with the CTS update from c378a32 → 4a82d78 in #9445.

Sample failure:

[fail] webgpu:api,operation,rendering,3d_texture_slices:one_color_attachment,mip_levels:format="r8unorm";mipLevel=0;depthSlice=1 (30ms). Log:
  - EXPECTATION FAILED: errors in texture: ()
      errors in mipLevel: 0
      texel at 2, 0, 0, sampleIndex: 0 expected: R: 0, actual: R: 0.501960813999176
      texel at 3, 0, 0, sampleIndex: 0 expected: R: 0, actual: R: 0.24705883860588074
      texel at 2, 1, 0, sampleIndex: 0 expected: R: 0, actual: R: 0.501960813999176
      texel at 3, 1, 0, sampleIndex: 0 expected: R: 0, actual: R: 0.24705883860588074
      texel at 2, 2, 0, sampleIndex: 0 expected: R: 0, actual: R: 0.501960813999176
      texel at 3, 2, 0, sampleIndex: 0 expected: R: 0, actual: R: 0.24705883860588074
        at AllFeaturesMaxLimitsGPUTest.expect (file:///home/runner/work/wgpu/wgpu/cts/out/common/framework/fixture.js:375:34)
        at checkTextureContent (file:///home/runner/work/wgpu/wgpu/cts/out/webgpu/api/operation/rendering/3d_texture_slices.spec.js:90:5)
        at eventLoopTick (ext:core/01_core.js:179:7)
        at async RunCaseSpecific.fn (file:///home/runner/work/wgpu/wgpu/cts/out/webgpu/api/operation/rendering/3d_texture_slices.spec.js:249:3)

https://github.com/gfx-rs/wgpu/actions/runs/24689498137/job/72207438665?pr=9445

[teoxoy]

This is probably due to gpuweb/cts#4625, the description of which hints at what we might be doing wrong:

There was an issue in some browsers where, when rendering to a slice of a 3d texture, they'd mark the entire texture as initialized even though only the individual slice was initialized.

Updated the tests so they check the entire texture. Also updated them to try every format.