Enable collect for multiple detectors

[abbiemery]

Description

Changes the collect method in bundler to handle the collection of multiple detectors. Contains the logic to collect stream resources using the maximum common number of frames written, determined by the minimum index.

Asset has been altered to only address a resource and datum and a new StreamAsset has been created to address stream_resource and stream_datum.

Motivation and Context

This enables logic to be moved out of Ophyd-async, generalising the process
Fixes #1649.

How Has This Been Tested?

TBC.

[danielballan]

Looks great. The effort on these tests is hugely valuable. I am suggested additional docstrings and added one comment on DocHolder for consideration, but I'm happy for this to go ahead.

[danielballan]

This is clever.

I'll mention that there is a utility in the test utils with a similar functionality, but I like the simplicity of this one.

It might be worth considering using collections.defaultdict(list) instead, which I think is a more "mainstream" / familiar way to achieve this, and refactoring assert_emitted into a function. On the other hand, I'm not sure that buys much over implementation here. Just a thought.

[coretl]

The choice between:

class DocHolder(dict):
    def append(self, name, doc):
        self.setdefault(name, []).append(doc)

    def assert_emitted(self, **numbers: int):
        assert list(self) == list(numbers)
        assert {name: len(d) for name, d in self.items()} == numbers

def test_plan():
    docs = DocHolder()
    RE(plan(), docs.append)
    docs.assert_emitted(start=1, descriptor=1, resource=1, datum=1, event=1, stop=1)

and

from collections import defaultdict

def assert_emitted(docs: Dict[str, list], **numbers: int):
    assert list(docs) == list(numbers)
    assert {name: len(d) for name, d in docs.items()} == numbers

def test_plan():
    docs = defaultdict(list)
    RE(plan(), lambda name, doc: docs[name].append(doc))
    assert_emitted(docs, start=1, descriptor=1, resource=1, datum=1, event=1, stop=1)

I think I marginally prefer the second, but not enough to change all the tests. @abbiemery I leave the choice up to you...

[danielballan]

I am in complete agreement. Slight preference, but not sure it's worth the effort to change.

[abbiemery]

Given the time pressure of these now, i'd rather make that a new issue to clean things up if it is preferred.