Add DB pool support

[Dimaz55]

Is your feature request related to a problem?

First of all "postgresql+asyncpg" scheme doesn't supported, second - I'm getting error when trying to run scheduler:
"sorry, too many clients already"

  File "/usr/local/lib/python3.13/site-packages/taskiq_pg/asyncpg/schedule_source.py", line 65, in get_schedules
    async with self._database_pool.acquire() as conn:
               ^^^^^^^^^^^^^^^^^^^
AttributeError: 'AsyncpgScheduleSource' object has no attribute '_database_pool'

Describe the solution you'd like

Support db pool

Describe alternatives you've considered

No response

Which component would this affect?

Scheduler Source

Use case

from sqlalchemy.ext.asyncio import create_async_engine

engine = create_async_engine(
    url="postgresql+asyncpg://postgres:postgres@localhost:5432/postgres",
    pool_size=50,
    max_overflow=10,
)

Additional context

No response

[danfimov]

First of all, the "postgresql+asyncpg" scheme is not supported.

Since the underlying asyncpg library does not support this scheme, this library does not support it either. I could theoretically modify the DSN before passing it to asyncpg, but for now, I think it is simply better to handle this in your code rather than in the library.

I'm getting an error when trying to run the scheduler: "sorry, too many clients already"

You can reduce the number of connections by setting max_size for the connection pool created inside the schedule source. However, I understand your concerns, and I will add the ability to use a provided connection pool in brokers, result backends, and schedule sources.

[danfimov]

Both fixes are landed in v0.9.0. So I will close this issue