fix: accept valid citation deltas in Amazon Bedrock streams (#18250)

## Background

Valid Bedrock citation-enabled streams emitted AI_TypeValidationError
events instead of accepting the provider's documented citation deltas.

## Root Cause

AmazonBedrockStreamSchema omitted citation from its contentBlockDelta
union. The live reproduction produced six citation validation errors,
and the focused schema-validation regression test failed before the
schema change.

## Summary

Added citation objects to the Bedrock stream schema, added regression
coverage, removed reproduction-only artifacts, and added a patch
changeset for @ai-sdk/amazon-bedrock.

## Testing

Added a streaming regression test that validates a representative
citation delta through AmazonBedrockStreamSchema and asserts that no
error part is emitted.

## End-to-end Validation

- `pnpm -C examples/ai-functions exec tsx -e '<live Bedrock citation
stream>'` — observed six live citation deltas and no type-validation
errors.

## Related Issues

Fixes #9101

Closes #18243

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Co-authored-by: ai-sdk-factory <308175966+ai-sdk-factory@users.noreply.github.com>
Co-authored-by: Lars Grammel <205036+lgrammel@users.noreply.github.com>
Co-authored-by: kamilKamilson <49162755+kamilKamilson@users.noreply.github.com>