[DOCS] Improve docs and minor fixes for testing.py and core.py

[lancerts]

Description

Update the docs and a test case to cover more dtypes.

Template

The core Triton is a small number of people, and we receive many PRs (thank
you!). To help us review your code more quickly, if you are a new
contributor (less than 3 PRs merged) we ask that you complete the following
tasks and include the filled-out checklist in your PR description.

Complete the following tasks before sending your PR, and replace [ ] with
[x] to indicate you have done them.

• I am not making a trivial change, such as fixing a typo in a comment.

• I have written a PR description following these
  rules.

• I have used an LLM to copyedit my PR description and and code comments.

• I have run pre-commit run --from-ref origin/main --to-ref HEAD.

• Select one of the following.

  • I have added tests.
    • /test for lit tests
    • /unittest for C++ tests
    • /python/test for end-to-end tests
  • This PR does not need a test because update a test case to cover more dtype.

• Select one of the following.

  • I have not added any lit tests.
  • The lit tests I have added are "minimal" -- they contain only the
    instructions necessary to exercise the bug. (Usually running Python code
    and using the instructions it generates is not minimal.)