Don't report a cancelled task as a refused refund

[zlexdev]

Refund.parse_result catches everything — funpaybotengine/methods/refund.py:42-49:

try:
    result = json.loads(response.raw_response)
except:
    raise RefundError(
        order_id=self.order_id,
        message=f"Unable to refund order {self.order_id}",
    )

CancelledError and KeyboardInterrupt derive from BaseException, so:

task = asyncio.create_task(bot.refund(order_id="..."))
task.cancel()          # -> RefundError("Unable to refund order ...")

The order may already be refunded. Refused and unknown arrive as the same
exception, and a caller retrying on RefundError retries a refund that went through.

The reason is dropped too — no from, nothing of the decode error — so an HTML login
page and a truncated body produce one identical sentence.

What changes

json.JSONDecodeError is caught specifically, its text goes into the message, and the
cause is chained. loggers.py gains methods_logger, following the one-per-subsystem
shape already there (session, router, dispatcher, runner); methods had none.

The raw body goes to DEBUG only, capped at 500 characters with the full length printed
beside it — when the answer is a login page it is a whole HTML document, and every failed
refund would put one in the log.

Tests

tests/test_refund.py, four tests. On the parent commit:

FAILED tests/test_refund.py::test_an_unparsable_answer_carries_why_and_chains_the_cause
FAILED tests/test_refund.py::test_cancellation_is_not_a_refused_refund
2 failed, 2 passed

ruff and mypy clean on the touched files. Pre-existing findings elsewhere are left
alone.