[HoodieStreamer] Register SparkWriteErrorValidator as default pre-commit validator

[shangxinli]

Summary

As part of #18765, HoodieStreamerWriteStatusValidator's error-check logic was migrated into explicit pre-commit orchestration steps in StreamSync, and a new SparkWriteErrorValidator was added to the validator framework as an opt-in.

The next step is to register SparkWriteErrorValidator as a default validator for HoodieStreamer, making it the canonical path.

Before doing so, we must ensure:

1. The hot path (no-validator config) does not error out due to default registration.
2. The Step 4 inline gate in StreamSync can then be retired once the default is stable.

Target

Next minor release.