feat: database connections and configurations

[cofin]

SQLSpec Configurations, Pools, and Connections.

This is a lot of foundational work for the next phases of development.

Driver	Database	Mode	Status
adbc	Postgres	Sync	✅
adbc	SQLite	Sync	✅
adbc	Snowflake	Sync	✅
adbc	DuckDB	Sync	✅
asyncpg	PostgreSQL	Async	✅
psycopg	PostgreSQL	Sync	✅
psycopg	PostgreSQL	Async	✅
aiosqlite	SQLite	Async	✅
sqlite3	SQLite	Sync	✅
oracledb	Oracle	Async	✅
oracledb	Oracle	Sync	✅
duckdb	DuckDB	Sync	✅
bigquery	BigQuery	Sync	🗓️ Planned
spanner	Spanner	Sync	🗓️ Planned
sqlserver	SQL Server	Sync	🗓️ Planned
mysql	MySQL	Sync	🗓️ Planned