Add 'om migrate stamp' command to mark migrations as applied

Summary

Add om migrate stamp command to mark migrations as applied without actually running them.

Use Cases

1. Importing existing schema: When adopting Redis OM on an existing database where indexes already exist
2. Manual migrations: When you've manually applied schema changes and need to update tracking
3. CI/CD workflows: Mark specific migration states for testing or deployment

Proposed Interface

# Mark all pending migrations as applied
om migrate stamp --all

# Mark specific migration as applied
om migrate stamp <migration_id>

# Mark up to a specific migration
om migrate stamp --target <migration_id>

Implementation Notes

• Add stamp method to SchemaMigrator that calls mark_applied() without running up()
• Add CLI command with appropriate options
• Similar to Alembic's stamp command

Start by locating SchemaMigrator and the existing migration CLI commands. Trace how migrations are marked applied and how CLI options are defined. Done means supporting stamp for all pending migrations, a specific migration, and a target without running up().