Improve unit test coverage

The unit test coverage was recently dramatically expanded, but there are still a few gaps.

- [ ] We are missing `typedSignatureHash` tests for array inputs.
- [ ] We aren't testing negative number inputs passed in as strings.
- [ ] We aren't testing numbers encoded as strings of odd v.s. even length.
- [ ] `personal_sign` isn't thoroughly tested in general (e.g. we only test '0x'-prefixed hex string inputs).
- [ ] Encryption isn't thoroughly tested (e.g. #75 )
- [ ] We don't have tests for naming collisions between custom types and Solidity types.
- [ ] We don't have any tests for arrays of a set size. We only have dynamic length array tests.
- [ ] We don't have tests for arrays of arrays.
- [ ] We don't have tests for custom types that behave like arrays.

Start by locating the existing unit tests covering typedSignatureHash, personal_sign, encryption, custom types, and array inputs. Run the current unit test suite to establish the baseline, then add focused cases for the unchecked scenarios in the issue. Done means each listed gap has coverage and the full suite passes.

Written by the indexing model from the issue text.