fix(gemini): normalize array-type nullable notation in SchemaMap prop…

[yondifon]

Description

Tested on gemini-2.5-flash & 'gemini-3-flash'

Gemini doesn't support the standard JSON Schema array-type notation for nullable fields:

{ "type": ["integer", "null"] }

It expects:

{ "type": "integer", "nullable": true }

This affects schemas passed as raw arrays — e.g. via Laravel AI SDK's ObjectSchema which wraps Illuminate's JsonSchema serializer:

public function schema(JsonSchema $schema): array
{
    return [
        'videoViews' => $schema->integer()->description('Total video views'),
        'averageWatchTime' => $schema->integer()->nullable()->description('Avg watch time in seconds'),
    ];
}

Laravel's serializer correctly follows JSON Schema draft-4 and converts nullable() to ["integer", "null"]. However, SchemaMap only normalizes properties when $this->schema instanceof ObjectSchema — raw array schemas bypass this branch and are spread into the payload as-is.

normalizeProperties() intercepts $schemaArray['properties'] before they reach Gemini, converting ["type", "null"] arrays into "nullable": true.

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Breaking Changes

None.