Add api to generate child keys from master key

[notmandatory]

Description

Add an API to bdk-ffi to derive a child key pair from a master extended key and a derivation path string (eg. "m/84'/1'/0'/0" or "m/84h/1h/0h/0"). Also test the new bdk-ffi functions and structs via the bdk-kotlin and/or bdk-swift projects. See the bdk-cli key -> derive subcommand as an example.

Expected Outcomes

• Update bdk.udl and lib.rs with functions and structs as needed
• Update bdk-kotlin or bdk-swift and add tests to cover new key generation functionality

Resources

• BDK Website
• BDK github repo
• BDK Discord
• uniffi-rs

Skills Required

• Experience with git. Guide
• Basic familiarity with rust. First seven chapters of the book
• Basic familiarity with Kotlin or Swift
• Familiarity with bitcoin descriptors and address generation

Mentor(s)

@artfuldev @notmandatory

Difficulty

Medium

Competency Test (optional)

• Install rust, compile bdk-ffi and build and test bdk-swift or bdk-kotlin.
• Read through the BDK docs.
• Install and run example bdk-kotlin or bdk-swift example wallet.
• Familiarity with basic rust, should be able to write basic structs and functions.