`defaultValue` is not honored for Python code generation

[bruno-f-cruz]

The device.yml already specifies a defaultValue field. The python interface supports it via a "default" keyword in the field constructor:

https://github.com/harp-tech/python/blob/d32971f3feba5b537d21df955b9f12b242d4292b/src/packages/harp-protocol/src/harp/protocol/_payload.py#L107

It would be nice to honor it in the generated code too. The runtime already supports it. From a quick test it looks like C# already supports it.

[glopesdev]

The default keyword works, but it belongs to a payload Field, so a plain scalar register has nowhere to carry it. PulseDOPort0 generates as RegisterU16, whose payload class is declared with scalar_dtype rather than a __value__ descriptor, and PayloadU16() requires a value.

Rather than converting those registers into __value__ payloads, one option is to generate the schema constraints as constants on the register class:

class PulseDOPort0(RegisterU16):
    address: ClassVar[int] = 42
    default_value: ClassVar[np.uint16] = np.uint16(1)
    min_value: ClassVar[np.uint16] = np.uint16(1)
    max_value: ClassVar[np.uint16] = np.uint16(65535)

This needs no runtime change and passes pyright. format() keeps meaning a Read, so no existing call changes meaning, and writing the default becomes PulseDOPort0.format(PulseDOPort0.default_value).

It also carries minValue and maxValue, which Python generates nowhere today while C# emits a Range attribute for them, and most of the register-level constraints in Behavior declare both. The C# register classes already expose Address, RegisterType and RegisterLength the same way.

The tradeoff is that this is discoverability rather than a calling convention, so nothing fills the value in for you.