Use rs-stellar-xdr for serialization/deserialization

[tluijken]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Feature

⤵️ What is the current behavior?

Currentely, the XDR deserialization and models are by our own custom implementation, which did not work properly yet.

🆕 What is the new behavior (if this is a feature change)?

RS-Stellar-XDR seems to provide the XDR deserialization features we need for our API. I've included this in our project and ensured it's deserialization features with unit tests. This can also be used as a reference.

💥 Does this PR introduce a breaking change?

Yes

🐛 Recommendations for testing

Run cargo test to see whether deserialization using the rs-stellar-xdr crate works.

📝 Links to relevant issues/docs

I think we should not try and reinvent the wheel here. rs-stellar-xdr looks promising. It has some great team members like Graydon Hoare (known for serde), and undergoes active development.

🤔 Checklist before submitting

• All projects build
• Follows style guide lines
• Relevant documentation was updated
• Rebased onto current main

[tluijken]

Was already implemented in main by @LeonardTibben. A rebase pretty much gave the same results.