test: add RC stress tests with large lists

- stress_rc.lux: Single-owner chains testing FBIP optimization
- stress_shared_rc.lux: Shared-reference chains (rc>1) forcing copy path

Both process lists of 100, 200, 500, and 1000 elements with map/filter/reverse.
Verifies no memory leaks with large data sets.

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

examples/stress_rc.lux

@@ -0,0 +1,24 @@
+// Stress test for RC system with large lists
+// Tests FBIP optimization with single-owner chains
+
+fn processChain(n: Int): Int = {
+    // Single owner chain - FBIP should reuse lists
+    let nums = List.range(1, n)
+    let doubled = List.map(nums, fn(x: Int): Int => x * 2)
+    let filtered = List.filter(doubled, fn(x: Int): Bool => x > n)
+    let reversed = List.reverse(filtered)
+    List.length(reversed)
+}
+
+fn main(): Unit = {
+    Console.print("=== RC Stress Test ===")
+
+    // Run multiple iterations of list operations
+    let result1 = processChain(100)
+    let result2 = processChain(200)
+    let result3 = processChain(500)
+    let result4 = processChain(1000)
+
+    Console.print("Completed 4 chains")
+    Console.print("Sizes: 100, 200, 500, 1000")
+}