Internal precompile binaries hook

[BitcoinZavior]

Precompiled Binaries Feature

Resolves #20
This PR introduces a comprehensive precompiled binaries system that significantly improves the developer experience by reducing build times and providing secure, signed artifacts.

Key Features

Secure Distribution

• Ed25519-signed precompiled binaries with public key verification
• Automated signing and verification pipeline
• Secure artifact hosting via GitHub Releases

Performance Improvements

• Skip local Rust compilation for supported platforms
• Automatic fallback to local builds when precompiled binaries unavailable
• Configurable modes: auto, always, or never

Developer Experience

• Zero-configuration setup for most users
• Comprehensive CLI tooling for maintainers
• Detailed documentation and troubleshooting guides

Configuration

Users can configure precompiled binaries in their pubspec.yaml:
Defaulting to auto which most users would want.

bdk_dart:
  precompiled_binaries:
    mode: auto  # auto | always | never