Improve unit test coverage

[Gudahtt]

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. Add working decryption failure test #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.