Round telemetry precision

[fresh3nough]

Summary

• round telemetry float values to fixed precision before send/serialize
• add shared telemetry precision helper
• update telemetry serializer tests for rounded values

Testing

• pio test -e native -f test_meshpacket_serializer (fails: pio not installed)

Co-Authored-By: Warp agent@warp.dev

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[github-actions]

@fresh3nough, Welcome to Meshtastic!

Thanks for opening your first pull request. We really appreciate it.

We discuss work as a team in discord, please join us in the #firmware channel.
There's a big backlog of patches at the moment. If you have time,
please help us with some code review and testing of other PRs!

Welcome to the team 😄

[caveman99]

Sorry, this is pointless. Over the air, floating point values are always the same size, as noted in the discussion.