- Add no_std support with std/alloc feature flags across all crates
- Bump version to 0.2.1 for kobe-core, kobe-btc, and kobe-eth
- Replace std imports with core/alloc equivalents throughout codebase
- Make random key generation optional via rand feature flag
- Add Wallet::from_entropy() method for custom entropy sources in no_std environments
- Move standard library error trait implementations behind std feature flag
- Update Cargo.toml dependencies