Add Rust ordered message stream implementation

[alxhill]

Changelog

Add OrderedMessageStream implementation for reading timestamp ordered messages in Rust.

Docs

Happy to add a docs change!

Description

The Python API allows reading in message-timestamp order:

todo

This PR brings roughly the same functionality to Rust:

todo

Before	After

Fixes: #659

[CLAassistant]

All committers have signed the CLA.

[jtbandes]

Thanks for spiking out this PR. At a quick glance, it looks like this is reading all messages into memory and storing them in a heap – is that right? If so, this would not be usable with larger MCAP files, so while it is a good proof of concept, I don't think it would make sense to include in the upstream repo. Did you have additional work planned on this PR?

[alxhill]

@jtbandes yeah good callout, I was looking at the Python implementation which I think roughly does the same thing iiuc.

The go implementation does not read everything in-memory, but does require a seekable stream - I think the challenge with not reading the whole stream in Rust is that LinearReader moves the buf pointer forwards, so there isn't a natural way to seek across chunks without a refactor. Does that seem correct or do you have thoughts on an alternative?

[jtbandes]

Looking at the Python now, it seems to only do the in-memory sort if using a NonSeekingReader; for a SeekingReader the ordering is handled by MessageQueue here: https://github.com/foxglove/mcap/blame/main/python/mcap/mcap/reader.py#L288

I'm not very familiar with the Rust implementation yet but it may be true that a refactor is needed - @james-rms may know more.