fix(0118): cast accepts compound type args; compound type literals are first-class Type values

examples/0182-types-cast-compound-types.sx

@@ -0,0 +1,27 @@
+// `cast(T) expr` accepts any compile-time-resolvable type argument,
+// including compound shapes: `*T`, `[*]T`, `?T`, `[]T`. The same lowering
+// makes a compound type literal a first-class `Type` value in expression
+// position (`t : Type = *s64;`), mirroring named types (`t : Type = f64;`).
+// Regression (issue 0118): compound casts fell into the runtime-dispatch
+// path and died with "unresolved 'unknown_expr'".
+
+#import "modules/std.sx";
+
+main :: () {
+    x := 42;
+    p : *s64 = @x;
+    q : *s64 = cast(*s64) p;        // no-op pointer cast
+    print("a: {}\n", q.*);
+    addr : s64 = xx p;
+    r : *s64 = cast(*s64) addr;     // int → ptr through compound cast
+    print("b: {}\n", r.*);
+    mp : [*]s64 = cast([*]s64) p;   // ptr → many-pointer
+    print("c: {}\n", mp[0]);
+    o : ?s32 = cast(?s32) 7;        // optional wrap
+    print("d: {}\n", o ?? -1);
+    arr := .[1, 2, 3];
+    s : []s64 = cast([]s64) arr;    // array → slice
+    print("e: {} {}\n", s.len, s[2]);
+    t : Type = *s64;                // first-class compound Type value
+    print("f: {}\n", type_name(t));
+}

examples/expected/0182-types-cast-compound-types.exit

@@ -0,0 +1 @@
+0

examples/expected/0182-types-cast-compound-types.stderr

@@ -0,0 +1 @@
+

examples/expected/0182-types-cast-compound-types.stdout

@@ -0,0 +1,6 @@
+a: 42
+b: 42
+c: 42
+d: 7
+e: 3 3
+f: *s64