Draft: re-organize things in re_log_encoding

[zehiko]

This is a heavy draft (things compile, but tons of broken link complaints), I spent some times re-organizing things so that everything related to rrd encoding ends up in the relevant module. This than ensures we only need to make the public interface actually public through relevant module exports. There's no new code, no publicly exposed functions were renamed (to confine the changes as much as possible to just this package, but things were moved around heavily.

To make sense of things, perhaps worth looking into lib.rs and what gets exposed and how.

We can drop this on the floor if we think it's not worth doing or doesn't make sense. My motivation was to not publicly expose guts of rrd protocol just because of module organization, but maybe it only makes sense to me.

Brief summary of changes:

• everything is moved under codec module. We already had file and wire there, but now we have rrd and wire
• all shared errors are at the codec errors now, same as Compression, VersionPolicy, etc
• anything related to rrd (encoders, decoders, public helper functions) is now in codec/rrd/encoder and codec/rrd/decoder and publicly exported to match the previous public export
• there was some naming conflict, for example encode for the previously public function and encode that is internally used. private encode is now encode_msg

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Result	Commit	Link	Manifest
✅	5a4d10f	https://rerun.io/viewer/pr/8797	+nightly +main

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