delete old crate locations, finalize workspace

[rnbguy]

remove the re-export shims that kept backward compat during migration. clean up build scripts.

changes

• delete app/, engine/, types/ directories
• update root Cargo.toml workspace members
• update Makefile build targets
• update scripts/spawn.bash, scripts/generate_testnet_config.sh for new binary path
• move utils/ -> crates/utils/
• solidity/, custom-reth/ stay at root