Added interior mutability test with UnsafeCell

Author: dkcumming

kmir/src/tests/integration/data/prove-rs/interior-mut3-fail.rs

@@ -0,0 +1,11 @@
+use std::cell::UnsafeCell;
+
+fn main() {
+    let data = UnsafeCell::new(0);
+    
+    unsafe {
+        *data.get() += 42;
+    }
+    
+    assert!(data.into_inner() == 42)
+}

kmir/src/tests/integration/data/prove-rs/show/interior-mut3-fail.expected

@@ -0,0 +1,16 @@
+
+┌─ 1 (root, init)
+│   #init ( symbol ( "interior_mut3_fail" ) globalAllocEntry ( 1 , Memory ( allocati
+│   function: main
+│   span: 67
+│
+│  (48 steps)
+└─ 3 (stuck, leaf)
+    rvalueAddressOf ( mutabilityNot , place ( ... local: local ( 1 ) , projection: p
+    span: 52
+
+
+┌─ 2 (root, leaf, target, terminal)
+│   #EndProgram
+
+

kmir/src/tests/integration/test_integration.py

@@ -436,7 +436,7 @@ def test_prove(spec: Path, tmp_path: Path, kmir: KMIR) -> None:
 
 PROVING_DIR = (Path(__file__).parent / 'data' / 'prove-rs').resolve(strict=True)
 PROVING_FILES = list(PROVING_DIR.glob('*.rs'))
-PROVE_RS_SHOW_SPECS = ['local-raw-fail', 'interior-mut-fail', 'interior-mut2-fail']
+PROVE_RS_SHOW_SPECS = ['local-raw-fail', 'interior-mut-fail', 'interior-mut2-fail', 'interior-mut3-fail']
 
 
 @pytest.mark.parametrize(