[yuxi-liu-wired]

Keep the sign of -0 in Value with arbitrary_precision

Without arbitrary_precision the integer literal -0 deserializes to
the float -0.0, so a Value keeps the sign. With the feature,
parse_any_number turned every integer that fits an i64 into
ParserNumber::I64 (d541381), and "-0".parse::<i64>() is 0, so the
sign was lost:

from_str::<Value>("-0")?            Number(0)    (should be -0)
to_string(&from_str::<Value>("[-0]")?)   "[0]"
from_value::<f64>(from_str("-0")?)  0.0          (from_str::<f64> gives -0.0)

-0 now stays in the textual representation, so it is written back as
-0 and converts to -0.0, matching the behaviour without the feature
and test_parse_negative_zero.

Test: test_negative_zero_value (fails before this change with
--features arbitrary_precision). Suite passes with no features,
arbitrary_precision, +raw_value, +preserve_order,float_roundtrip, and
raw_value,preserve_order.

Testing

Each commit adds a regression test that fails before the change. The full test suite passes and
cargo fmt --check is clean on the changed files.

Found with a differential fuzzer comparing serde_json, simd-json, sonic-rs and jiter.

[dtolnay]

Thanks!