Remove unused scope PoolRepository.by_source_project

Summary

Removes the unused scope PoolRepository.by_source_project from app/models/pool_repository.rb.

Related to #542966 (closed)

Verification

This scope was verified as unused by:

• keela --type scopes flagged it as unused
• Grep search found no callers (the finder's by_source_project_id is an unrelated _id-suffixed private method)
• Not used in scope chaining
• Not used in merge() calls
• Not used as default_scope or association scope (EE mixin only adds a delegate)

Cascade Removals

None - this was a standalone removal.

The scope's only usage was a single spec example, so that describe '.by_source_project' block was removed along with its now-orphaned lets (another_pool_repository / project2).

Metrics

Source File Complexity (flog)

Metric	Before	After	Improvement
File flog total	134.0	131.3	-2.7 (2.0%)
Scope flog score	2.6	N/A	-2.6 removed

Spec File Complexity (flog)

Metric	Before	After	Improvement
Spec file flog total	747.6	717.5	-30.1 (4.0%)
Spec block flog score	10.2	N/A	-10.2 removed

Test Suite Impact

• Specs removed: 1 example
• Spec file: spec/models/pool_repository_spec.rb
• Time saved per run: 0.05456 seconds

Estimated CI Savings

Estimate	Pipelines/Month	Time Saved	Cost Saved/Month	Cost Saved/Year
Pessimistic	15,000	0.23 hrs/month	$0.41	$4.91
Moderate	30,000	0.45 hrs/month	$0.82	$9.82
Optimistic	50,000	0.76 hrs/month	$1.36	$16.37

Based on 0.05456 seconds saved per pipeline × $0.03/minute (large runners: 3x cost factor on $10/1000 base minutes)

Files Modified

• app/models/pool_repository.rb (scope removed - 1 line)
• spec/models/pool_repository_spec.rb (specs removed - 16 lines, 1 example)
• scripts/lint/keela_baseline.yml (entry removed - 2 lines)

Related

• Related to #542966 (closed) (Improve unused helper methods workflow)
• Part of dead code cleanup effort
• Scope was listed in scripts/lint/keela_baseline.yml