test: add FBIP and RC verification test cases

Add test cases demonstrating FBIP (Functional But In-Place) optimization:
- test_fbip_clean.lux: Basic FBIP chain (map, filter, reverse)
- test_fbip_allocs.lux: Single-owner allocation test with range/map/filter/reverse
- test_no_fbip.lux: Demonstrates shared reference forcing rc>1 path
- test_rc_comparison.lux: Comparison of FBIP vs non-FBIP allocations

All tests verify no memory leaks with the RC system.

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

examples/test_rc_comparison.lux

@@ -0,0 +1,17 @@
+fn main(): Unit = {
+    Console.print("=== Allocation Comparison ===")
+    
+    // FBIP path (rc=1): list is reused
+    Console.print("Test 1: FBIP path")
+    let a1 = List.range(1, 50)
+    let b1 = List.map(a1, fn(x: Int): Int => x * 2)
+    let c1 = List.reverse(b1)
+    Console.print("FBIP done")
+    
+    // To show non-FBIP, we need concat which doesn't have FBIP
+    Console.print("Test 2: Non-FBIP path (concat)")
+    let x = List.range(1, 25)
+    let y = List.range(26, 50)
+    let z = List.concat(x, y)  // concat always allocates new
+    Console.print("Concat done")
+}