pymavlink: read/set params improvements

Existing docs could be updated to make use of [`master.param_fetch_*`](https://github.com/ArduPilot/pymavlink/blob/master/mavutil.py#L519-L535), and [`master.param_set_send`](https://github.com/ArduPilot/pymavlink/blob/master/mavutil.py#L543-L552) or [`pymavlink.mavparm.MAVParmDict.mavset`](https://github.com/ArduPilot/pymavlink/blob/master/mavparm.py#L10-L71).

Would also be good to format the output values as floats, since not all parameters are integers (as brought up [here](https://discuss.bluerobotics.com/t/set-thrusters-to-run-with-a-pilot-input-gain-less-than-25/10547/2)). Likely worth changing to `.format` syntax (or `f-strings`, but since they require Python >= 3.6 they aren't compatible with the current companion, so would only work on the surface computer or a companion with a [more recent Python version](https://discuss.bluerobotics.com/t/updating-python-in-companion/10398/2))

Start by reviewing the existing parameter read/set documentation, then compare it with the referenced APIs in mavutil.py and mavparm.py. Update the examples to cover parameter fetching and setting, and ensure displayed parameter values are formatted as floats using syntax compatible with the supported Python versions.

Written by the indexing model from the issue text.