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/tailcall.lux

@@ -0,0 +1,50 @@
+// Demonstrating tail call optimization (TCO) in Lux
+// TCO allows recursive functions to run in constant stack space
+//
+// Expected output:
+// factorial(20) = 2432902008176640000
+// fib(30) = 832040
+// sumTo(1000) = 500500
+// countdown(10000) completed
+
+// Factorial with accumulator - tail recursive
+fn factorialTCO(n: Int, acc: Int): Int =
+    if n <= 1 then acc
+    else factorialTCO(n - 1, n * acc)
+
+fn factorial(n: Int): Int = factorialTCO(n, 1)
+
+// Fibonacci with accumulator - tail recursive
+fn fibTCO(n: Int, a: Int, b: Int): Int =
+    if n <= 0 then a
+    else fibTCO(n - 1, b, a + b)
+
+fn fib(n: Int): Int = fibTCO(n, 0, 1)
+
+// Count down - simple tail recursion
+fn countdown(n: Int): Int =
+    if n <= 0 then 0
+    else countdown(n - 1)
+
+// Sum with accumulator - tail recursive
+fn sumToTCO(n: Int, acc: Int): Int =
+    if n <= 0 then acc
+    else sumToTCO(n - 1, acc + n)
+
+fn sumTo(n: Int): Int = sumToTCO(n, 0)
+
+// Test the functions
+let fact20 = factorial(20)
+let fib30 = fib(30)
+let sum1000 = sumTo(1000)
+let countResult = countdown(10000)
+
+// Print results
+fn printResults(): Unit with {Console} = {
+    Console.print("factorial(20) = " + toString(fact20))
+    Console.print("fib(30) = " + toString(fib30))
+    Console.print("sumTo(1000) = " + toString(sum1000))
+    Console.print("countdown(10000) completed")
+}
+
+let output = run printResults() with {}