H2 connection management utilities.

H2 database adapter - main entry point implementing the DBAdapter protocol.

This namespace serves as the main entry point for H2 database
functionality, implementing the DBAdapter protocol and coordinating
specialized modules for different aspects of H2 operations.

The adapter has been refactored into 5 specialized namespaces:
- h2.connection: Connection management and H2-specific settings
- h2.query: H2-specific query building and boolean handling
- h2.metadata: Table introspection and schema information
- h2.utils: Utility functions and DDL helpers
- h2.core: Main adapter implementation and coordination (this namespace)

Key Features:
- PostgreSQL compatibility mode for easier migration
- In-memory databases for fast testing
- File-based databases for development
- Standard SQL features with good performance
- Native boolean support (no conversion needed)

H2-Specific Optimizations:
- PostgreSQL compatibility mode by default
- Proper timezone handling
- Case-insensitive identifiers for compatibility
- Optimized connection pool settings for embedded usage

H2 metadata and table introspection utilities.

H2 query building utilities.

H2 utility functions and DDL helpers.