packet.rs: add cfgtimemode2 and cfgtimemode3 frames

[gwbres]

Hello @lkolbly @reitermarkus ,

congratulations for this amazing lib 🚀 🛰️ !

With this contribution, I would like to introduce two configuration frames that are specific to Timing class receivers:

• CfgTmode2
• CfgTmode3

For datafields that might have two roles, like ecef_x_or_lat_hp (ECEF coordinates or latitude coordinate), I use a scaling of 1.0 and documented the units properly.

I closed the previous pull request because I had too much rework to reach something valuable.

[lkolbly]

Thank you! Sorry it's taken me so long to get to your PRs

[gwbres]

Thank you! Sorry it's taken me so long to get to your PRs

Hello @lkolbly,
No worries, I can still have our application rely on my fork. But with the latest contributions, this is already looking quite good. I will look into in details, thank you for spending some time on this