make $lib.tags.prefix a no-op on null names

[mikemoritz]

Summary

• $lib.tags.prefix now treats a (null) names argument as a no-op and returns an empty list, matching the convention used by $list.extend() (toiter(..., noneok=True)).
• Updated the _storm_locals arg description to document the null behavior; autodoc picks this up.
• Added a null-input assertion next to the existing $lib.tags.prefix tests.

Test plan

• python -m pytest -n auto synapse/tests/test_lib_stormtypes.py::StormTypesTest::test_storm_lib_base

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.49%. Comparing base (9e39276) to head (377da9f).
⚠️ Report is 1 commits behind head on synapse-3xx.

Additional details and impacted files

@@             Coverage Diff              @@
##           synapse-3xx    #4917   +/-   ##
============================================
  Coverage        96.48%   96.49%           
============================================
  Files              258      258           
  Lines            63301    63301           
============================================
+ Hits             61078    61080    +2     
+ Misses            2223     2221    -2     

Flag	Coverage Δ
linux	96.49% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.