Fix detached taql docstring (docs build)

[barrettp]

Phase 377 inserted _taql_check_tablerefs between the taql docstring and its method, silently dropping the docstring (Documenter: no docs found for 'taql'). Moved the helper above the docstring; a scan of src/ and ext/ finds no other docstring followed by a comment; local docs/make.jl builds with no errors.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.99%. Comparing base (1f51cfa) to head (b0e63cf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #120      +/-   ##
==========================================
- Coverage   96.02%   95.99%   -0.03%     
==========================================
  Files          52       52              
  Lines       10576    10574       -2     
==========================================
- Hits        10156    10151       -5     
- Misses        420      423       +3     

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