Add Morningstar ProStar MPPT charge controller preset

[pbitzer]

Summary

• Adds complete device preset for the Morningstar ProStar MPPT solar charge controller
• Uses IEEE 754 half-precision float (input_type = "e") for measurement registers, verified against the official Modbus spec (MS-001723 v05)
• Reads 61 contiguous registers (0x0010-0x004C) covering 54 data channels: voltages, currents, temperatures (including 3-phase inductor temps), charge/load status, Ah/kWh accumulators, MPPT sweep results, and daily statistics

Key design decisions

• Float16 not fixed-point: The ProStar MPPT stores measurement values as IEEE 754 half-precision floats, unlike the SunSaver which uses fixed-point n * scale * 2^-15. Using input_type = "e" lets Python's struct module decode them directly with no conversion math needed.
• input_type not binary_type: Required for Modbus presets because Brokkr's ModbusInput sets a default input_type = "H" that would override binary_type. This matches the sunsaver's approach.
• 32-bit accumulators (Ah counters, hourmeter, alarm): Use input_type = "I" with HI-word-first ordering, matching the spec's big-endian layout.

Test plan

• Verify TOML parses without errors
• Confirm register count (61) matches the contiguous block 0x0010-0x004C
• Test on actual ProStar MPPT hardware if available
• Verify float16 decoding produces correct engineering values

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