feat: refactor AlgorithmicEvaluator to stateless, add game engine module and holdem_sim CLI

- Refactor AlgorithmicEvaluator from stateful Arc<Evaluator> wrapper to
  pure stateless evaluator with zero-allocation construction
- Extract shared evaluation logic into pub(crate) methods, eliminating
  ~220 lines of duplicated code from Evaluator
- Add game module: table, hand runner, tournament, bots, config, stats
- Add holdem_sim CLI binary crate for running simulations
- Convert MathEvaluator to thread-safe singleton with Arc<Inner> pattern
- Replace heap-allocated combination generation with const-generics
  stack-based approach in AlgorithmicEvaluator::evaluate_n_card_hand
- Add thiserror 2 dependency for GameError derive
- Update docs: README, ACHIEVEMENTS, ROADMAP

holdem_sim/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "holdem_sim"
+version = "0.1.0"
+edition = "2021"
+description = "Texas Hold'em simulation runner"
+
+[[bin]]
+name = "holdem_sim"
+path = "src/main.rs"
+
+[dependencies]
+holdem_core = { path = "../holdem_core" }
+clap = { version = "4", features = ["derive"] }