fix: keep -0 and +0 distinct through serialize/deserialize

[greymoth-jp]

serialize memoizes every value it has seen in a Map so shared references and cycles round-trip as one record. Map keys use SameValueZero, which treats -0 and +0 as the same key, so when both appear in one value the second one reuses the first one's record. After deserialize they come back with a single sign:

const {serialize, deserialize} = require('@ungap/structured-clone');

deserialize(serialize([-0, 0]));        // [-0, -0]   (expected [-0, 0])
deserialize(serialize([0, -0]));        // [0, 0]     (expected [0, -0])
deserialize(serialize({neg: -0, pos: 0})); // {neg: -0, pos: -0}

Native structuredClone and this module's own default clone (which copies values directly instead of going through the memo) both keep the two zeros distinct, so serialize/deserialize is the only path that loses the difference.

The fix skips the memo for negative zero only, so -0 can never share a record with +0. Every other value memoizes exactly as before, so reference sharing, cycles and the existing serialized output are unchanged. A Set still collapses -0/+0 into one element, matching native, because that happens in the Set itself and not in the memo.

Added a round-trip test alongside the Invalid Date one. The suite passes; reverting the serialize.js change makes the new test fail.

[WebReflection]

I would do that only if TYPE is number and it's falsy otherwise this is a huge performance loss

[greymoth-jp]

Gated the -0 check so Object.is only runs on zero-valued numbers now, everything else short-circuits before it, so the per-value cost is gone. Existing tests plus the -0/+0 round-trip pass. Thanks for the review.