climate: Add halves when divider is at least 2

[3v1n0]

Various climate devices use a temperature divider of 2, and they do allow use of halves values, however current tuyaha doesn't allow this.

As per this, add an has_halves function that will return true for multiple of 2, while fix target_temperature_step() so that it returns the proper value depending we support decimals or halves

[ollo69]

I think that this PR should be closed because obsolete.