Add plan mode support to SQL registry for feature view versioning #6104

Summary

The proto-based (file) registry supports feast plan which shows a dry-run diff of what would change before feast apply. The SQL registry does not yet have equivalent plan mode support for the feature view versioning flow.

This includes:

• Showing version changes (pin/revert) in plan output for the SQL registry
• Surfacing FeatureViewPinConflict errors during feast plan (not just feast apply)
• Ensuring the SQL registry's diff logic accounts for version metadata

Context

Feature view versioning (PR #6101) added version tracking with pin/revert support. The pin conflict detection was added to both the file registry and SQL registry's apply_feature_view, but the plan mode path (which previews changes without applying) only works with the file registry today.

Acceptance criteria

• feast plan correctly previews version pin/revert operations when using the SQL registry
• FeatureViewPinConflict is raised during plan (not just apply) for the SQL registry
• Plan output shows version metadata changes (e.g., "driver_stats: v1 → v0 (pin)")
• Tests cover plan mode with SQL registry for versioning scenarios