fix(dashboard): round heater power setting to 3 decimals

Koushik Kumaranrequested to merge
315-round-heater-power-setting into main

Converting the power setting from W to mW introduced floating point noise (e.g. 249.90000000000003), which was displayed verbatim in the editable power field. Round to 3 decimals wherever the setting is derived from the backend.

Closes #315 (closed)

Closes #315 (closed)

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