Implements filtering tests for mag/min/mipmapFilters with additional float32-filterable formats.

[lokokung]

Issue: #2072

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located in the test tree.
• Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Helpers and types promote readability and maintainability.

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[lokokung]

Ah, sorry it too so long to fix! Pretty much needed to rewrite all the min/magFilter tests in order to differentiate between mirror-repeat and clamp-to-edge. We can chat offline more if there's anything in the tests that is too confusing!

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[austinEng]

LGTM! thank you for the incredible comments and diagrams explaining the tests!