Charging improvements

[jkaflik]

Context

Current firmware has basic charge control with fixed thresholds and EMA-filtered ADC readings. Upstream OpenMower LowLevel has more operational behavior around charge retry, regen, and high-level configurable limits.

Current Local Behavior

• Reads battery voltage, charge voltage, and charge current.
• Enables charging based on fixed cutoffs from src/hardware.h.
• Publishes basic power topics.
• Uses EMA filtering.

Upstream Reference Behavior

OpenMower LowLevel:

• Uses configurable v_charge_cutoff, i_charge_cutoff, and v_battery_cutoff.
• Disables charging when limits are exceeded.
• Retries charging after a delay instead of continuously toggling.
• Keeps charge path enabled for regen when not docked.
• Supports an option to ignore charge current if needed.

Acceptance Criteria

• Add a charge retry delay after charging is disabled by cutoff conditions.
• Preserve or explicitly evaluate upstream regen behavior when no charger/dock voltage is present.
• Make charge thresholds configurable from ROS 2 or document why compile-time constants are sufficient for now.
• Avoid rapid charge-enable toggling around thresholds.
• Publish whether charging is currently allowed/enabled separately from charger presence.
• Review fixed thresholds in src/hardware.h against upstream defaults and HW 0.13.x expectations.

Notes

This should remain conservative. If there is uncertainty around safe thresholds, prefer disabling charging and surfacing the reason in telemetry.