fast filtering on phase current values

[Gabrielerusso]

Implemented light filtering on phase current readings

• Added a 3‑sample sliding window average followed by two cascaded first‑order low‑pass filters.
• Designed to be computationally efficient with minimal phase delay.
• Filtering smooths noisy current measurements while raw values are still used for overcurrent protection, so safety mechanisms remain unaffected.

Also does sampling only when needed, saving some clock cycle.