AP_Rangefinder Lightware Lidar GRF 500 Driver Update Rate Parameter Set Improperly

## Bug Report

### Issue details

There is an error in the [grf 500 datasheet](https://lightwarelidar.com/wp-content/uploads/2025/12/GRF-500-Product-Guide-Rev-1.2.pdf) that has caused the error in the driver. The datasheet contains the following statement: `Writing this command will set the update rate in Hz. Adjustable from 0.5 Hz to 10 Hz in 0.1 Hz increments.` and yet the value described is a float and stored in a uint32 format.

The GRF 500 interprets the update rate field not as hertz but deci-hertz. This has been confirmed by setting the RNGFNDx_GRF_RATE to 50 (its default) and using the Lightware studio software via serial passthrough to read back the value. In this case the value reads back as 5 hz instead of 50 hz.

Also the RNGFNDx_GRF_RATE parameter can not set the full range of values accepted by the update rate parameter for the GRF 500 as it cannot set values less than 1 hz. (minimum value supported is 0.5 hz)

It is likely the case that this field is interpreted differently for the GRF 250 vs GRF 500 as the [grf 250 datasheet](https://lightwarelidar.com/wp-content/uploads/2025/12/GRF-250-Product-Guide-v5.2.pdf) contains the following statement `Writing this command will set the update rate in Hz. Adjustable from 1 Hz to 50 Hz in 1 Hz increments.` I do not have a GRF 250 to test with so i cannot say for certain.

I will reach out to lightware support and post updates.

@rishabsingh3003

**Version**
latest

**Platform**
[ ] All
[ ] AntennaTracker
[x] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

**Airframe type**
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**Hardware type**
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**Logs**
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