Gemini ToolPayloadMapper generates invalid tools schema (functionDeclarations must be array, not object)

The class `\NeuronAI\Providers\Gemini\ToolPayloadMapper` generates an invalid Gemini tools schema. `"tools": { "functionDeclarations": { "items": { ... } } }` However, Gemini requires `functionDeclarations` to be an `array of function declaration objects`, not an object keyed by function name. Because of this mismatch, Gemini rejects the payload with: `Invalid JSON payload received. Unknown name "items" at 'tools.funct...` ### Expected behavior `ToolPayloadMapper` should generate: `"tools": { "functionDeclarations": [ { "name": "items", "description": "Description", "parameters": { ... } } ] } ` ### Steps to reproduce 1. Implement any toolkit using `ToolkitInterface` 2. Allow NeuronAI to generate the Gemini schema 3. Send the schema to the Gemini `generateContent` endpoint 4. Receive 400 error: `Invalid JSON payload received. Unknown name "items"`