Replace hardcoded async DSN rewrite with dialect-aware helper

[myyong]

Summary

The async connection string is built by a hardcoded string replacement in datafaker/utils.py:

async_dsn = db_dsn.replace("postgresql://", "postgresql+asyncpg://")

This has two failure modes for any non-PostgreSQL connection:

1. Silently broken for MS-SQL: an mssql:// DSN passes through unchanged and is handed to create_async_engine, which then fails with a confusing dialect error rather than a clear message.
2. Silently broken when a driver is already specified: a DSN such as postgresql+psycopg2://... does not match the literal postgresql:// prefix, so the replace is a no-op and the sync driver is passed to the async engine.

Proposed steps

1. Introduce a make_async_dsn(db_dsn: str) -> str helper that parses the DSN with SQLAlchemy's make_url, extracts the dialect (the portion before any +), and rewrites the drivername component using a lookup table:

   from sqlalchemy.engine import make_url
   
   _ASYNC_DRIVER_MAP = {
       "postgresql": "postgresql+asyncpg",
       "mssql": "mssql+aioodbc",
   }
   
   def make_async_dsn(db_dsn: str) -> str:
       url = make_url(db_dsn)
       dialect = url.drivername.split("+")[0]
       async_driver = _ASYNC_DRIVER_MAP.get(dialect)
       if async_driver is None:
           raise ValueError(
               f"No async driver is registered for dialect '{dialect}'."
           )
       return str(url.set(drivername=async_driver))

   This correctly handles postgresql://, postgresql+psycopg2://, mssql://, and mssql+pyodbc:// — and raises a clear ValueError for unknown dialects instead of producing a silent no-op.

2. Replace the call site in create_db_engine (datafaker/utils.py):

   # before
   async_dsn = db_dsn.replace("postgresql://", "postgresql+asyncpg://")
   engine = create_async_engine(async_dsn, **kwargs)
   
   # after
   engine = create_async_engine(make_async_dsn(db_dsn), **kwargs)

3. Add aioodbc as an optional dependency (see Add MS-SQL driver support (pyodbc/pymssql) #93) for the mssql extra so the async MS-SQL driver is available when needed.

4. Add unit tests covering:

   • postgresql:// → postgresql+asyncpg://
   • postgresql+psycopg2:// → postgresql+asyncpg://
   • mssql:// → mssql+aioodbc://
   • mssql+pyodbc:// → mssql+aioodbc://
   • Unknown dialect raises ValueError
   • Credentials, host, port, and database name are preserved through the rewrite

Acceptance criteria

• create_db_engine produces a valid async DSN for both postgresql:// and mssql:// connection strings.
• A DSN with an explicit driver (e.g. postgresql+psycopg2://) is correctly rewritten rather than silently passed through.
• Passing an unsupported dialect raises a ValueError with a message naming the dialect.
• All existing PostgreSQL async tests continue to pass.

Related

• Add MS-SQL driver support (pyodbc/pymssql) #93 — MS-SQL driver dependency (adds pyodbc/aioodbc)