Fix #5141: Add option to disable Gemini intermediate reasoning streaming

[roomote]

Fixes issue #5141 by adding geminiDisableIntermediateReasoning setting to suppress malformed intermediate reasoning chunks that cause errors. When enabled, reasoning still works but intermediate results aren't streamed. Includes comprehensive tests.

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Important

Adds geminiDisableIntermediateReasoning setting to control streaming of reasoning chunks in GeminiHandler, with comprehensive tests.

• Behavior:
  • Adds geminiDisableIntermediateReasoning setting in provider-settings.ts to control streaming of intermediate reasoning chunks.
  • When enabled, suppresses reasoning chunks in GeminiHandler in gemini.ts.
• Tests:
  • Adds tests in gemini.spec.ts to verify behavior with and without geminiDisableIntermediateReasoning enabled.
  • Tests ensure correct chunk processing and suppression of reasoning chunks when setting is enabled.

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[delve-auditor]

✅ No security or compliance issues detected. Reviewed everything up to 8e233b3.

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• 🔎 Scanned files: 3 changed file(s)

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