PHPLIB-1739 Add builder support for the vectorSearch search operator

[GromNaN]

• https://jira.mongodb.org/browse/PHPLIB-1739
• DRIVERS-3309 Add vectorSearch search operator mql-specifications#45

[Copilot]

Pull request overview

Adds Atlas Search builder support for the $search stage’s vectorSearch operator, including fixture pipelines and tests to assert correct serialization.

Changes:

• Introduces a new VectorSearchOperator builder for $search: { vectorSearch: ... }.
• Exposes the operator via MongoDB\Builder\Search::vectorSearch() factory method.
• Adds pipeline fixtures and PHPUnit coverage for ANN/ENN examples (including filter usage).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

File	Description
tests/Builder/Search/VectorSearchOperatorTest.php	Adds coverage for building $search.vectorSearch pipelines (ANN basic/filter + ENN).
tests/Builder/Search/Pipelines.php	Adds expected JSON fixtures for the new vector search operator pipelines.
src/Builder/Search/VectorSearchOperator.php	Implements the new search operator builder and argument validation for list vectors.
src/Builder/Search/FactoryTrait.php	Adds vectorSearch() factory method to construct the new operator.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.69%. Comparing base (8da0d3d) to head (16d9465).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/Builder/Search/VectorSearchOperator.php	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               v2.x    #1908   +/-   ##
=========================================
  Coverage     87.69%   87.69%           
- Complexity     3356     3360    +4     
=========================================
  Files           457      458    +1     
  Lines          6702     6714   +12     
=========================================
+ Hits           5877     5888   +11     
- Misses          825      826    +1     

Flag	Coverage Δ
6.0-replica_set	86.55% <91.66%> (+<0.01%)	⬆️
6.0-server	82.63% <91.66%> (+0.01%)	⬆️
6.0-sharded_cluster	86.34% <91.66%> (+<0.01%)	⬆️
8.0-replica_set	87.56% <91.66%> (+<0.01%)	⬆️
8.0-server	83.36% <91.66%> (+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.

[alcaeus]

LGTM pending merge of the upstream pull request