Math brute force - distinguish between fp16, fp32 and fp64 in results

The results (JSON) file produced for the math brute force tests does not distinguish between testing of fp32 and fp64 (and the testing of fp16 being added in issue #528 and pull request #587).

This differs from the integer tests, which _do_ distinguish between testing with different integer width (at least for some of the tests).

Start with the math brute force tests and the JSON results they produce, then compare their precision handling with the integer tests, which distinguish integer widths. Confirm how fp16, fp32, and fp64 are represented and update the results so each precision is distinguishable; done when the generated JSON clearly separates all three.

Written by the indexing model from the issue text.