Fix minor bugs in RFComms plugin

[mkrizmancic]

🦟 Bug fix

Fixes #1738

Summary

Fixes 3 minor bugs in RFComms plugin:

1. Incorrect usage of standard deviation and variance in Gaussian noise generation
2. Incorrect calculation of sending and receiving bitrates
3. Incorrect calculation of the message size

More information and description of proposed solutions implemented in this PR for all three bugs can be found in #1738.

Additionally, there is a small change in the warning messages for bitrate limitation. Warning messages now specify which Radio/Model (robot in simulation) has broken the limit.

Checklist

• [x] Signed all commits for DCO
• [ ] Added tests
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.