fix(core): fix decimal string IntOrHex parsing

[Rjected]

Motivation

Previously, we would parse decimal strings like "100000" as hex, because they did not match a raw serde_json::Number variant in IntOrHex. This caused problems when parsing genesis fields with from_int_or_hex, for example:

            "alloc": {
                "0x3E951C9f69a06Bc3AD71fF7358DbC56bEd94b9F2": {
                  "balance": "1000000000000000000000000000"
                },
             }

This would parse "1000000000000000000000000000" instead as 0x1000000000000000000000000000.

This did not fail U256 parsing because its FromStr implementation accepts both 0x-prefixed and non-0x-prefixed strings, and will deserialize both as hex.

Solution

Check for 0x prefixes in from_int_or_hex and from_u64_or_hex if the value matches a String instead of serde_json::Number. If there is a prefix, deserialize as hex. Otherwise, the value deserializes as a decimal string.

Tests are added for the failing Genesis alloc, and unit tests for the from_int_or_hex method itself are added.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[gakonst]

@mattsse

[gakonst]

cc @prestwich for ethers-next, you wouldn't believe how much time pinpointing this took us