Support async dbapi for SQLite

Describe the bug Trying to use an AsyncEngine with SQLite raises an AwaitRequired exception. I don’t see anything specifically about async support in the SQLite dialect docs, but SQLite did work with async in 1.4.0b1.

Expected behavior For create_async_engine("sqlite:///:memory:") to provide a usable AsyncEngine.

To Reproduce This code runs fine with 1.4.0b1 but fails with 1.4.0b2:

import asyncio
import sqlalchemy
from sqlalchemy.ext.asyncio import create_async_engine

metadata = sqlalchemy.MetaData()
vals = sqlalchemy.Table(
    "vals",
    metadata,
    sqlalchemy.Column("id", sqlalchemy.Integer, primary_key=True),
)

async def main():
    engine = create_async_engine("sqlite:///:memory:")
    async with engine.begin() as conn:
        await conn.run_sync(metadata.create_all)
        res = await conn.execute(vals.insert().values())
        print(res.inserted_primary_key)

if __name__ == "__main__":
    asyncio.run(main())

Error

Traceback (most recent call last):
  File "/tmp/asynctest.py", line 23, in <module>
    asyncio.run(main())
  File "/usr/lib/python3.9/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
    return future.result()
  File "/tmp/asynctest.py", line 18, in main
    res = await conn.execute(vals.insert().values())
  File "/tmp/asynctest/lib/python3.9/site-packages/sqlalchemy/ext/asyncio/engine.py", line 404, in execute
    result = await greenlet_spawn(
  File "/tmp/asynctest/lib/python3.9/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 121, in greenlet_spawn
    raise exc.AwaitRequired(
sqlalchemy.exc.AwaitRequired: The current operation required an async execution but none was detected. This will usually happen when using a non compatible DBAPI driver. Please ensure that an async DBAPI is used. (Background on this error at: http://sqlalche.me/e/14/xd1r)

Versions.

• OS: Linux, Debian Bullseye
• Python: 3.9.1
• SQLAlchemy: 1.4.0b2
• Database: SQLite
• DBAPI: pysqlite

[CaselIT]

The wip in gerrit more or less works, but has some problems in the tests that I was not able to solve. IIRC it seemed to leak connections what are not closed leading to the interpreter not closing, but I’m not sure if it’s the sqlalchemy test suite fault and aiosqlite is simpy very sensitive to it, the integration code or aiosqlit. I’ll try to look again into it

[zzzeek]

if aiosqlite is using a thread I’m a little non-optimistic it can handle a lot of requests but let’s see!