This implements the F32Interval class and fundamental accuracy
functions described in my prototype for reworking,
#1402, how floating point tests are
written.

This also adds in testing that did not appear in my prototype.

There are a couple of functions that are not currently used that I
have included in this patch that have suppressions for unused-vars on
them. I included them in this patch since they are logically grouped
with this code. These supressions will be removed in future patches.

Issue #792

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.

When landing this PR, be sure to make any necessary issue status updates.