DOC: keep Hypothesis strategy examples readable

[nightcityblade]

Description

Closes #11465.

The introductory Hypothesis examples now generate variables without arbitrary attributes. This keeps the examples varied while preventing recursively generated metadata from overwhelming the rendered user guide. The later section that explains attribute strategies remains unchanged.

Checklist

• Closes Testing secting is user guide renders incorrectly #11465
• Tests added — N/A; this is a documentation-only rendering change.
• User visible changes (including notable bug fixes) are documented in whats-new.rst — N/A; no runtime behavior changes.
• New functions/methods are listed in api.rst — N/A; no API changes.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
    Tools: Codex. I reviewed the complete diff and validated generated examples locally.

[nightcityblade]

CI follow-up: the only failing job completed 21,383 tests and then hit RuntimeError: error during blosc decompression: 0 in TestZarrRegionAuto::test_zarr_region_chunk_partial_offset[2]. This is unrelated to this docs-only change (doc/user-guide/testing.md); all other CI jobs passed. I attempted to rerun the failed job, but contributors do not have permission to rerun upstream workflows, so a maintainer rerun is needed.

[eni-awowale]

Rerunning the job is still failing. I am going to merge the main branch into your branch. There are some tests failing in main right now though but we know it's unrelated.

Otherwise everything else looks good.

[eni-awowale]

Not sure why the docs build is failing. @dcherian have any ideas?

[nightcityblade]

I checked the raw Read the Docs log. The changed doc/user-guide/testing.md notebook executed successfully (9.01s). The warnings-as-errors failure comes from unrelated files: the io.md notebook hits AttributeError: set_auto_chartostring inside the ncdata/Iris integration, and the StringAccessor docstring emits two docutils errors plus a warning. Since this PR only changes testing.md, there does not appear to be a PR-side docs fix to make here.