Store timestamps in nanosecond precision

We currently store timestamps in float format while most interfaces and log formats use some integer representation. Converting these to floating point is a lossy operation.

My proposal is to add an additional `timestamp_ns` argument and attribute to the Message class. On initialization, if the `timestamp` argument is given it would be converted to ns. The `.timestamp` attribute can be dynamically calculated on get and set.

It would be fairly trivial to update the interfaces and log formats to use ns timestamps instead.

Start by locating the Message class and reading how its timestamp is initialized, stored, and exposed. Then trace the interfaces and log formats mentioned in the proposal to identify every timestamp boundary. Done means nanosecond values remain lossless while existing timestamp access continues to work consistently across those interfaces and formats.

Written by the indexing model from the issue text.