Closes #9578

Summary

High-throughput VCF to PostgreSQL loader using asyncpg for bulk variant ingestion.

• Adds vcfpgloader/load module for loading VCF variants into PostgreSQL databases
• Uses cyvcf2 for VCF parsing and asyncpg for high-performance database operations
• Supports batch loading with configurable batch size and parallel workers
• Outputs JSON report with loading statistics and detailed log

Test plan

• Stub tests pass with sarscov2 and homo_sapiens test data
• nf-core modules lint vcfpgloader/load passes (43/43 tests)
• Pre-commit hooks pass