Fix KEV filter performance regression in findings endpoints

[nscuro]

Description

Fixes KEV filter performance regression in findings endpoints.

Turns out the exact count via window function could force a more optimal query plan. The KEV filter now drives from a materialized array so the query planner cannot degrade it to point-lookups for every single finding.

Addressed Issue

Relates to #7035

Additional Details

N/A

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have updated the migration changelog accordingly
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly
• This PR is a substantial change (per the ADR criteria), and I have added an ADR under docs/adr/

[owasp-dt-bot]

✅ Snyk checks have passed. No issues have been found so far.

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✅	Open Source Security	0	0	0	0	0 issues

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 complexity

Metric	Results
Complexity	0

View in Codacy

🟢 Coverage ∅ diff coverage · +0.02% coverage variation

Metric	Results
Coverage variation	✅ +0.02% coverage variation (-1.00%)
Diff coverage	✅ ∅ diff coverage (70.00%)

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (2300b79)	44504	38808	87.20%
Head commit (7219a21)	44504 (+0)	38817 (+9)	87.22% (+0.02%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#7036)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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