Index-based message retrieval for mcap #11

The single-channel OSITrace implementation supports index-based message retrieval, whereas the python mcap library does not support this feature out of the box. This is a reminder to either provide a change request to the python mcap library or implement it on our side.

Exploratory draft for implementation of indexing for mcaps: https://github.com/OpenSimulationInterface/osi-python/tree/feature/indexed-mcap-reader.