chore: consolidate prettierignore and prettierrc files

[feywind]

Fixes googleapis/librarian#4581 🦖

[feywind]

Remaining errors:

1. presubmit/units - logging-bunyan has an outstanding issue with punycode:

026-04-15T19:57:36.2128760Z   1) Uncaught error outside test suite:
2026-04-15T19:57:36.2130078Z      Uncaught DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
2026-04-15T19:57:36.2130978Z       at node:punycode:7:10

2. OwlBot is having issues running the types script in bigquery, and a mismatch between OwlBot's linter and the linter used in-project is causing it to erroneously detect dangling Promises. The types script works fine when run manually, and the linter lines have been overridden for now.

3. Core presubmit is failing due to the sinon pin error. The issue here is that gax pulls a copy of the latest release of google-cloud-speech and tries to build it; the latest release does not have the sinon pin, so it fails. Ignoring this.

[feywind]

Split into the two sub-PRs.