Restore init=False dataclass fields when converting from JSON

[Kayvan-Zahiri]

A dataclass with a field(init=False) can be encoded but not decoded. The JSON encoder includes every field, and value_to_type then passes all of them to the constructor, which rejects the non-init ones:

@dataclass
class Order:
    id: str
    attempts: int = field(init=False, default=0)

# workflow/activity arg or result of type Order
TypeError: Order.__init__() got an unexpected keyword argument 'attempts'

I hit this on 1.34.0 with DataConverter.default round-tripping a plain dataclass like the one above.

The fix keeps init=False fields out of the constructor call. If the payload has a value for one, it's converted with the field's type hint like any other field and set after construction. object.__setattr__ is used so frozen dataclasses work too. Without that last step a field set after __init__ (like a counter) would silently reset to its default on decode.

Added test_json_dataclass_non_init_fields_round_trip in tests/test_converter.py, covering a field computed in __post_init__, a field changed after construction, and a frozen dataclass. It fails on main with the TypeError above and passes with the fix.

Validation:

• pytest tests/test_converter.py: 41 passed
• ruff check, ruff format --check, basedpyright and mypy --namespace-packages --check-untyped-defs on the changed files: clean. pyright is clean on _payload_converter.py. On tests/test_converter.py it only reports pytest as an unresolved import, which it also does on main in my env.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}