Add wgpu Hybrid browser tests to `vello_sparse_tests`

[ajakubowicz-canva]

This task tracks a followup to #1020 (comment)

Currently wasm-pack test --chrome --features webgl tests the WebGL renderer backend.

Completion criteria of this task depends on the command wasm-pack test --chrome testing the wgpu backend with WebGPU enabled. Currently this command will fail. I believe it simply detects 0 tests.

[ajakubowicz-canva]

Consider the following refactor: #1020 (comment)