feat: Add CockroachDB vector database support

[viragtripathi]

 Implements comprehensive CockroachDB integration with these features:

 Core Features:
 - CockroachDB vector index support using C-SPANN algorithm (v25.2+)
 - Production connection pooling (100+ base connections, configurable)
 - Automatic retry logic for transient errors (40001, 40003)
 - Multi-region resilience with proper error handling
 - Support for L2, Cosine, and Inner Product distance metrics
 - Vector index tuning (partition size, beam size parameters)
 - Filter support (NumGE, StrEqual)

 Implementation:
 - vectordb_bench/backend/clients/cockroachdb/cockroachdb.py: Main client with retry logic
 - vectordb_bench/backend/clients/cockroachdb/config.py: Configuration classes
 - vectordb_bench/backend/clients/cockroachdb/db_retry.py: Retry decorator with exponential backoff
 - vectordb_bench/backend/clients/cockroachdb/cli.py: CLI parameter definitions
 - tests/test_cockroachdb.py: Comprehensive test suite
 - pyproject.toml: Added cockroachdb optional dependencies

 References:
 - CockroachDB Vector Indexes: https://www.cockroachlabs.com/docs/stable/vector-indexes
 - Retry Best Practices: https://cockroachlabs.com/docs/stable/advanced-client-side-transaction-retries

[viragtripathi]

/assign @XuanYang-cn

[alwayslove2013]

@viragtripathi Thank you so much for your contribution!

We noticed there are some conflicts in this pull request. Could you please resolve them? After that, we'll be happy to merge it.

[viragtripathi]

@viragtripathi Thank you so much for your contribution!

We noticed there are some conflicts in this pull request. Could you please resolve them? After that, we'll be happy to merge it.

@alwayslove2013 Thank you!
I've resolved the conflicts by rebasing on the latest main branch. The implementation is ready for review and merge. Please let me know if you need any changes!

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: alwayslove2013, viragtripathi
To complete the pull request process, please assign xuanyang-cn after the PR has been reviewed.
You can assign the PR to them by writing /assign @xuanyang-cn in a comment when ready.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment