Abstract tasks

[hugiron]

Idea:
Call tasks from third-party microservices.

Solution:
Add abstract tasks that can be defined in third-party services or a separate library.

Example:

# On third-party service or library
@broker.abc.task()
async def dist_sum(a: int, b: int) -> int:
    ...

task = await dist_sum.kiq(1, 2)
result = await task.wait_result(timeout=2)

# On worker
@broker.task()
async def dist_sum(a: int, b: int) -> int:
    return a + b

# or

from mylib import dist_sum  # abstract task from library

@dist_sum.register()
async def _(a: int, b: int) -> int:
    return a + b