Reject out-of-range JSON numbers instead of silently serializing them as null

`parse_number` accepts the result of Rust's f64 parser without checking finiteness. A syntactically valid large exponent such as `1e9999` can produce infinity. The writer replaces non-finite `Json::Num` values with `null`, so parse/write can silently change a number into a different JSON type. The existing f64 representation needs a clear unsupported-range error rather than silent conversion.

Source evidence at the head of #520:

- [utils/src/json.rs:220](https://github.com/wavefnd/Wave/blob/2ae0a91c57fd76323124c0e4dff552adbfadbe1b/utils/src/json.rs#L220) — `s.parse::()`
- [utils/src/json.rs:289](https://github.com/wavefnd/Wave/blob/2ae0a91c57fd76323124c0e4dff552adbfadbe1b/utils/src/json.rs#L289) — `if n.is_finite()`

Acceptance:

- [ ] Reject a parsed non-finite numeric result with an actionable range error; a new arbitrary-precision dependency is not required.
- [ ] Cover positive/negative overflowing exponents and the largest supported finite values.
- [ ] Verify accepted finite number round trips remain numeric, including negative zero according to the current writer policy.
- [ ] Do not expand this patch into changing the public Json representation or all number formatting.

API/reference context: [JSON permits implementations to bound numeric range, section 6](https://www.rfc-editor.org/rfc/rfc8259.html#section-6).

Related: #351 is independent string-decoding work.

Audit status: identified by static source inspection; the scenarios above have not been executed during this audit. The permalink fixes the reviewed revision; this report does not claim the defect was introduced by #520.

Start in utils/src/json.rs at parse_number around line 220, then inspect the writer's non-finite-number handling around line 289. Run or add focused JSON parser tests for positive and negative overflowing exponents, largest finite values, finite round trips, and negative zero; done means non-finite results produce an actionable range error without changing the public Json representation.

Written by the indexing model from the issue text.