fix: prevent recursive Google tool schemas from aborting model calls (#19490)

## Background

Recursive Zod tool schemas caused @ai-sdk/google to abort generateText
and streamText during request preparation, preventing any provider
request.

## Root Cause

Google tool preparation always converted schemas to its
OpenAPI-compatible format, whose cycle detection throws
UnsupportedFunctionalityError for recursive local references; the
reproduction confirmed requests were never sent.

## Summary

Recursive schemas now fall back to Google's parametersJsonSchema field,
while non-recursive schemas retain existing conversion behavior. Added a
patch changeset.

## Testing

Added tool-preparation and request-body regression tests verifying
recursive schemas are preserved and requests proceed.

## End-to-end Validation

- `pnpm -C examples/ai-functions exec tsx --eval '<recursive
generateText/streamText validation>'` — both calls reached mocked Google
requests, preserved the recursive schema, and returned tool calls.

## Related Issues

Fixes #19488

Closes #19489

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Co-authored-by: ai-sdk-factory <308175966+ai-sdk-factory@users.noreply.github.com>
Co-authored-by: wottpal <3930150+wottpal@users.noreply.github.com>