fix(api): return 422 for missing fetcher query params

[bozarnr]

Closes #7629. Maps missing required fields from fetcher QueryParams validation to HTTP 422 and adds a focused regression test. Tests: pytest targeted regression; ruff targeted files.

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[Copilot]

Copilot review overview

🔵 Needs a closer look

Preserve the parameter source for missing body fields and add body regression coverage.

Review effort: Lite
Findings: None

What changed in this PR

This PR updates API validation so missing fetcher parameters return HTTP 422 instead of 500.

Changes:

• Adjusts missing-field validation handling.
• Adds regression coverage for missing category.

File	Summary
openbb_platform/​core/​tests/​api/​test_exception_handlers.py	Adds regression coverage for missing fetcher parameters.
openbb_platform/​core/​openbb_core/​api/​exception_handlers.py	Updates validation-error classification.

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