Add more favorite functions

[rolandwalker]

Description

This still has little/subtle effects, as the final sort is dominated by shortest-first and other rules. But I have hopes to apply this more strongly, and wanted to get a basic list on record.

Covered under the existing changelog.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

1. Missing targeted test for the new behavior (low)
   • The PR’s functional change is expanding favorite_functions, which affects function completion ranking in normal SQL contexts (sqlcompleter.py:855).
   • The only test update is in a backticked-column completion snapshot (test_smart_completion_public_schema_only.py:739), which is indirect and won’t catch regressions in actual function suggestion ordering.
   • Action: add a direct test in function context (for example select f... / select co...) asserting favorites are prioritized as intended.

No correctness or security issues stood out in the changed code itself.

I could not run the test suite in this environment because pytest/uv are unavailable.