Feature request: make setpoint step size configurable

[PetePeter]

Problem

The setpoint number entity has "step": 0.01 hardcoded in number.py. This means dashboard pickers increment in 0.01°C steps, which is unnecessarily precise for a room temperature target and makes the slider fiddly to use.

Proposed solution

Expose step (and optionally min/max) as an option in the config flow so users can set their preferred increment without patching the integration source.

Minimal change — add a setpoint_step field to the config/options flow with a sensible default (e.g. 0.5) and wire it through to the number entity descriptor:

# number.py
{
    "key": "setpoint",
    "step": config_entry.options.get("setpoint_step", 0.5),  # was hardcoded 0.01
    ...
}

Workaround

Currently requires patching number.py directly, which gets overwritten on every HACS update.

Context

• HA 2026.5.1
• simple_pid_controller installed via HACS
• Use case: per-room temperature setpoints in 0.5°C increments

Thanks for the integration — works great otherwise!