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_fbip_allocs.lux

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+// This test shows FBIP optimization by comparing allocation counts
+// With FBIP (rc=1): lists are reused in-place
+// Without FBIP (rc>1): new lists are allocated
+
+fn main(): Unit = {
+    Console.print("=== FBIP Allocation Test ===")
+    
+    // Case 1: Single owner (FBIP active) - should reuse list
+    let a = List.range(1, 100)
+    let b = List.map(a, fn(x: Int): Int => x * 2)
+    let c = List.filter(b, fn(x: Int): Bool => x > 50)
+    let d = List.reverse(c)
+    Console.print("Single owner chain done")
+    
+    // The allocation count will show FBIP is working
+    // if allocations are low relative to operations performed
+}

examples/test_fbip_clean.lux

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+fn main(): Unit = {
+    // Test FBIP without string operations
+    let nums = [1, 2, 3, 4, 5]
+    let doubled = List.map(nums, fn(x: Int): Int => x * 2)
+    let filtered = List.filter(doubled, fn(x: Int): Bool => x > 4)
+    let reversed = List.reverse(filtered)
+    let len = List.length(reversed)
+    Console.print("done")
+}

examples/test_no_fbip.lux

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+// Test WITHOUT FBIP by forcing rc>1 (shared reference)
+fn useList(l: List<Int>): Int = {
+    List.length(l)
+}
+
+fn main(): Unit = {
+    Console.print("=== Without FBIP (forced rc>1) ===")
+    
+    let a = List.range(1, 100)
+    // Create alias to bump rc, preventing FBIP
+    let alias = a
+    let len1 = useList(alias)
+    
+    // Now 'a' has rc>1 so map must allocate new list
+    let b = List.map(a, fn(x: Int): Int => x * 2)
+    let c = List.filter(b, fn(x: Int): Bool => x > 50)  
+    let d = List.reverse(c)
+    
+    Console.print("Shared reference chain done")
+}

examples/test_rc_comparison.lux

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+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")
+}