feat: add initial execution framework

[mtshit]

Summary

• add the initial execution engine crate
• add the strategy helper crate, tests, and examples

Verification

• cargo fmt --all --check
• cargo clippy --workspace --all-features --all-targets -- -D warnings
• cargo test --workspace --all-features
• cargo test --workspace --all-features --examples

This is the first code PR after the non-code bootstrap commit.