Add precision parameter to dsmr sensor

[zumitnl]

Description:

I was working with the DSMR sensor for reading the power and gas usage.
It uses floats with 3 digits and was filling up the database really quickly.
I've added the precision parameter to make the number of digits configurable.
It works now beter with the value 2.

First I changed it in the file after every update, but I've tried to do my first pull request for this to fix this into the future.

Related issue (if applicable): fixes #

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#8106

Example entry for configuration.yaml (if applicable):

# Power (DSMR)
- platform: dsmr
  port: /dev/ttyUSB1
  dsmr_version: 5
  precision: 2

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[homeassistant]

Hi @zumitnl,

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[dgomes]

Instead of passing the full config object in to the device entity, you could just pass the precision.

[zumitnl]

I've tested the precision parameter also with the latest version 0.86.4.
What is the next step?

[MartinHjelmare]

Looks good! @dgomes are you ok with this?