Adding descriptor generator

[AmosOO7]

Description

This PR introduces a new descriptor subcommand to the BDK CLI that enables users to generate Bitcoin wallet descriptors for internal and external paths, supporting common BIP standards (44, 49, 84, 86). It includes support for both single-path and multipath descriptors using an extended key (tprv/tpub).

This resolves issue #175

Note: The --weak option for string-based key generation is intentionally excluded in this PR, pending further instruction.

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Features Implemented

• descriptor subcommand
• Supports BIP44, BIP49, BIP84, and BIP86 script types
• Generates internal and external descriptors
• Supports --multipath for wildcard derivation paths
• Rejects mismatched key-network pairs (e.g., xprv on testnet)
• Reasonable defaults:
  • --type defaults to 84
  • --network default testnet
  • --multipath defaults to false

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Usage Examples

1. Generate a Private Key (Seed Phrase)

cargo run key generate --entropy 12

2. Generate Descriptors from a Provided Private Key

cargo run -- --network testnet descriptor --type <example: 44, 49, 84, 86,> <XPRV>

Generate a Descriptor from a Seed Phrase (no key provided)

cargo run -- --network testnet descriptor --type 84

Generate Multipath Descriptor from Xpub key

cargo run -- --network testnet descriptor --type 84 --multipath <XPUB>

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature
• I've updated CHANGELOG.md

[tvpeter]

Good work Amos.

Most of the fns in utils should be in the handlers file, while most of those in handlers should be placed in the utils.