Provide a low-level api to write multiple non-contiguous byte-slices into a message

[alokpr]

Currently mcap::Writer provides an API where the message body is a single contiguous slice. This forces the client to create a new byte array if the original message contains multiple slices. For example, see zenoh::Sample whose payload can consist of non-contiguous data slices.

The proposed API can follow the existing pattern used by attachment:

• start_message(header)
• put_message_bytes(slice)
• finish_message()

[jtbandes]

Some other prior art, https://developer.apple.com/documentation/foundation/data also allows non-contiguous regions

[alokpr]

Should we create a tracking issue for this feature request if you are aligned?

[amacneil]

Note from discussion - this is for the rust library

[bennetthardwick]

Hey sorry @alokpr there was an internal thread about this but I never responded here. I've created #1392 as a tracking issue.