Add binary codec support for MPT

[pwang200]

We use xrpl-rust in Craft, the tool for xrpl programability. It'd be great to be able to use xrpl-rust to decode MPT data. Thanks!

[sappenin]

FWIW, here's some prior art from the other SDKs for adding MPT support:

• xrpl-py: Initial feature (some other enhancements)
• xrpl4j: Initial feature
• xrpl-js:Initial feature (some other enhancements)