feat: Serde Serialize and Deserialize traits for the RbTree in the ic-certified-map crate.

[levifeldman]

This change adds the CandidType, serde Serialize and Deserialize traits to the RbTree in the ic-certified-map crate.
Useful for serializing a canister's certified data during upgrades.

This PR changes the 'static generic lifetime bounds on the RbTree impl blocks and replaces it with a custom lifetime 't.

How Has This Been Tested?

library/ic-certified-map/src/rbtree/test.rs

Checklist:

• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation.

[adamspofford-dfinity]

This should probably be implemented as a plain map serialization rather than encoding the full tree structure. Unlike the HashTree structure, the RbTree internal structure is not relevant to the user.

[levifeldman]

Hey, I replaced the 'static generic lifetime bounds on the RbTree impl blocks for a custom lifetime 't.

[levifeldman]

and added a test

[levifeldman]

Looks like the new canister import functionality is messing with the PR check: https://github.com/dfinity/cdk-rs/actions/runs/6156757139/job/16706101327?pr=399

[levifeldman]

Hey @adamspofford-dfinity, can you merge this?

[levifeldman]

Thanks Adam @adamspofford-dfinity for the review and merge.

My apologies for putting off addressing your feedback for a while there. Won't happen again.