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_core/tests/integration_tests.rs

@@ -424,8 +424,8 @@ pub struct IntegrationTestResults {
     pub passed_tests: usize,
     /// Number of failed tests
     pub failed_tests: usize,
-    /// Test execution time in milliseconds
-    pub execution_time_ms: u64,
+    /// Test execution time in microseconds
+    pub execution_time_us: u64,
 }
 
 impl IntegrationTestSuite {
@@ -479,7 +479,7 @@ impl IntegrationTestSuite {
             total_tests,
             passed_tests,
             failed_tests,
-            execution_time_ms: elapsed.as_millis() as u64,
+            execution_time_us: elapsed.as_micros() as u64,
         };
 
         println!("Integration tests completed: {:?}", results);
@@ -733,6 +733,6 @@ mod tests {
 
         let results = results.unwrap();
         assert!(results.total_tests > 0);
-        assert!(results.execution_time_ms > 0);
+        assert!(results.execution_time_us > 0);
     }
 }