chore: use EmptyPathSeq() everywhere and NewLocalContext() for tests

[barakmich]

One existing helper (now used everywhere) and one new helper to reduce test boilerplate.

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.50%. Comparing base (9171c3f) to head (608505f).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/query/context.go	89.48%	2 Missing ⚠️
pkg/query/intersection.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2811      +/-   ##
==========================================
- Coverage   78.52%   78.50%   -0.02%     
==========================================
  Files         459      459              
  Lines       44448    44467      +19     
==========================================
+ Hits        34898    34903       +5     
- Misses       6723     6733      +10     
- Partials     2827     2831       +4     

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[tstirrat15]

LGTM!