fix: custom Type serialization methods

[Rhodanthe1116]

Summary for #199 and Proposed Solutions

Original Problem

• The to_json method of Type works as expected, but to_xml does not.
• For xml attribute ex: <tag time="2012"/> , serialization relies only on to_s or a raw string, which is insufficient for certain use cases (e.g., custom serialization for specific types). Fix specs reqif#1
• Additionally, the from_{format} methods of Type (e.g., from_xml, from_json) do not function as expected. While this issue isn't directly addressed in this PR, tests have been included to document the problem (currently commented out).

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Changes Introduced in This PR

1. Added Specs for Issue #199

• to_xml and to_json overrides:
  • Created tests for overriding these methods for a simple custom type.
• HighPrecisionDateTime example:
  • Added an example using Ceramic and HighPrecisionDateTime to demonstrate correct serialization/deserialization as part of the documentation (e.g., in README.md).

2. Applied serialize in Three Areas

• xml element:
• xml attribute:
• json

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Considerations and Next Steps

• Discussion Needed:
  • These changes may affect other parts of the project or introduce unexpected behavior, as I am new to the codebase.
• Unresolved Issues:
  • The from_{format} methods (e.g., from_xml, from_json) of Type are still not functioning as intended. Tests documenting this issue are included but commented out.

[ronaldtse]

@HassanAkbar I believe this PR is superseded by #224, is that correct? If so please help close this. Thanks!

[HassanAkbar]

Closing this one in favor of #271.