✨ UTF-8 Simplification

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Suggestion

Because of other serialization changes, the changes to serialize.hpp might be able to be simpler.

static string toJson(const electionguard::Manifest &serializable)

In line 591, the regex might not be needed because of changes that were made on the c# side.

return regex_replace(manifestStr, regex("\\\\\\\\u"), "\\u");

### Possible Implementation

_No response_

### Anything else?

_No response_