Bulk enqueueing

[RealOrangeOne]

Currently, the API only supports enqueuing one task at a time. For most use cases, this is fine, however for larger-scale deployments, it would be handy to schedule multiple tasks at once (akin to bulk_create in the ORM).

[RealOrangeOne]

Proposal:

Add a prepare method to a Task which returns a PreparedTask, holding the arguments provided and other task metadata. A sequence of these can be passed to bulk_enqueue on the task to be enqueued:

my_task.bulk_enqueue([
    my_task.prepare(1, {"2": 3}),
    my_task.prepare(4, {"5": 6}),
])

There's a potential foot-gun with this approach, in how modified attributes (ie .using are handled). Using those on the PreparedTask makes sense (ie my_task.using(...).prepare), although it could easily be missed if someone decides to use my_task.using(...).bulk_enqueue, as they'd be silently ignored. Perhaps we need to track if the task is "pure", and only allow one side to have modifications (either the prepared task or the task calling bulk_enqueue)