feat: modernize sqlglot builder paths

[cofin]

Summary

• update temporal, vector-distance, Postgres, and Spanner generator registrations to use the builder-local helper

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.90%. Comparing base (a876f40) to head (8a820ff).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #524      +/-   ##
==========================================
+ Coverage   74.87%   74.90%   +0.02%     
==========================================
  Files         441      442       +1     
  Lines       55085    55120      +35     
  Branches     8689     8697       +8     
==========================================
+ Hits        41245    41287      +42     
+ Misses      11156    11148       -8     
- Partials     2684     2685       +1     

Flag	Coverage Δ
integration	58.63% <71.79%> (-0.03%)	⬇️
py3.10	71.78% <100.00%> (+0.03%)	⬆️
py3.11	71.80% <100.00%> (+0.03%)	⬆️
py3.12	71.80% <100.00%> (+0.03%)	⬆️
py3.13	71.80% <100.00%> (+0.03%)	⬆️
py3.14	74.03% <100.00%> (+0.03%)	⬆️
unit	61.91% <100.00%> (+0.04%)	⬆️

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Files with missing lines	Coverage Δ
sqlspec/builder/__init__.py	100.00% <ø> (ø)
sqlspec/builder/_explain.py	98.42% <100.00%> (+0.02%)	⬆️
sqlspec/builder/_generation.py	100.00% <100.00%> (ø)
sqlspec/builder/_join.py	66.21% <100.00%> (+0.30%)	⬆️
sqlspec/builder/_merge.py	75.50% <100.00%> (-0.33%)	⬇️
sqlspec/builder/_parsing_utils.py	66.66% <100.00%> (+7.93%)	⬆️
sqlspec/builder/_temporal.py	85.71% <100.00%> (+11.13%)	⬆️
sqlspec/builder/_vector_distance.py	80.64% <100.00%> (-0.13%)	⬇️
sqlspec/core/statement.py	85.18% <100.00%> (+0.27%)	⬆️
sqlspec/dialects/postgres/_generators.py	85.71% <100.00%> (ø)
... and 2 more

... and 2 files with indirect coverage changes

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