fix: make all example programs work correctly

- Add string concatenation support to + operator in typechecker
- Register ADT constructors in both type environment and interpreter
- Bind handlers as values so they can be referenced in run...with
- Fix effect checking to use subset instead of exact match
- Add built-in effects (Console, Fail, State) to run block contexts
- Suppress dead code warnings in diagnostics, modules, parser

Update all example programs with:
- Expected output documented in comments
- Proper run...with statements to execute code

Add new example programs:
- behavioral.lux: pure, idempotent, deterministic, commutative functions
- pipelines.lux: pipe operator demonstrations
- statemachine.lux: ADT-based state machines
- tailcall.lux: tail call optimization examples
- traits.lux: type classes and pattern matching

Add documentation:
- docs/IMPLEMENTATION_PLAN.md: feature roadmap and status
- docs/PERFORMANCE_AND_TRADEOFFS.md: performance analysis

Add benchmarks for performance testing.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

examples/functional.lux

@@ -1,4 +1,12 @@
 // Demonstrating functional programming features
+//
+// Expected output:
+// apply(double, 21) = 42
+// compose(addOne, double)(5) = 11
+// pipe: 5 |> double |> addOne |> square = 121
+// curried add5(10) = 15
+// partial times3(7) = 21
+// record transform = 30
 
 // Higher-order functions
 fn apply(f: fn(Int): Int, x: Int): Int = f(x)
@@ -12,31 +20,43 @@ fn addOne(x: Int): Int = x + 1
 fn square(x: Int): Int = x * x
 
 // Using apply
-let result1 = apply(double, 21)  // 42
+let result1 = apply(double, 21)
 
 // Using compose
 let doubleAndAddOne = compose(addOne, double)
-let result2 = doubleAndAddOne(5)  // 11
+let result2 = doubleAndAddOne(5)
 
 // Using the pipe operator
-let result3 = 5 |> double |> addOne |> square  // ((5 * 2) + 1)^2 = 121
+let result3 = 5 |> double |> addOne |> square
 
 // Currying example
 fn add(a: Int): fn(Int): Int =
     fn(b: Int): Int => a + b
 
 let add5 = add(5)
-let result4 = add5(10)  // 15
+let result4 = add5(10)
 
 // Partial application simulation
 fn multiply(a: Int, b: Int): Int = a * b
 
 let times3 = fn(x: Int): Int => multiply(3, x)
-let result5 = times3(7)  // 21
+let result5 = times3(7)
 
 // Working with records
 let transform = fn(record: { x: Int, y: Int }): Int =>
     record.x + record.y
 
 let point = { x: 10, y: 20 }
-let sum = transform(point)  // 30
+let recordSum = transform(point)
+
+// Print all results
+fn printResults(): Unit with {Console} = {
+    Console.print("apply(double, 21) = " + toString(result1))
+    Console.print("compose(addOne, double)(5) = " + toString(result2))
+    Console.print("pipe: 5 |> double |> addOne |> square = " + toString(result3))
+    Console.print("curried add5(10) = " + toString(result4))
+    Console.print("partial times3(7) = " + toString(result5))
+    Console.print("record transform = " + toString(recordSum))
+}
+
+let output = run printResults() with {}