The test 'test_inf_stays_string_for_integer_only' incorrectly asserted
that _coerce_number('inf') returns float('inf'), but the function
correctly returns the original string 'inf' because infinity is not
JSON-serializable.
Fixed the assertion to expect the string 'inf', and added two new tests
for negative infinity and NaN edge cases to improve coverage of the
non-JSON-serializable number guard in _coerce_number().
vominh1919
652f8e6f3e