Structs, arrays, owned strings, memory model, modules, debug info

- struct with default values; constructors Point(1, 2) / Point(x: 1); field access, auto-deref through pointers
- []T arrays with bounds checks, literals, for-each, push/pop/insert/remove/clear/resize/find/contains/join/slice/reverse/sort
- str carries its length: .len, s[i], +, comparison, sub/find/split/trim/upper/lower/replace/repeat/bytes, str(x), int(s), float(s)
- Memory: values own their memory and are freed at the end of their block; assignment copies, temporaries move;
  parameters are lent and only copied when the function changes them; defer; new()/free() for manual heap memory
- input(), read_file/write_file/file_exists, exit(), fn main([]str args)
- Finch modules: import name, module.fn(), module.Struct
- C structs from headers (fields, fixed arrays, nested); passed and returned by value with the System V x86-64 ABI;
  addr(fn) gives C a callback
- link "file.c" compiles and links your own C code
- -g emits DWARF debug info (gdb/lldb)
- Small C runtime (runtime/finch_rt.c) embedded in the compiler, cached in ~/.cache/finch
- Tests: 58, all clean under valgrind (MEMCHECK=1 tests/run.sh)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/structs.fn

@@ -0,0 +1,49 @@
+// Structs, arrays of structs, and a linked list on the heap.
+import "math.h"
+
+struct Point {
+    float x
+    float y
+}
+
+struct Shape {
+    str name
+    []Point corners
+    int color = 0xFF8800
+}
+
+struct Node {
+    int value
+    ptr[Node] next
+}
+
+fn perimeter(Shape s) -> float {
+    total := 0.0
+    for i in 0..s.corners.len {
+        a := s.corners[i]
+        b := s.corners[(i + 1) % s.corners.len]
+        dx := b.x - a.x
+        dy := b.y - a.y
+        total += sqrt(dx * dx + dy * dy)
+    }
+    return total
+}
+
+fn main() {
+    square := Shape(name: "square", corners: [Point(0, 0), Point(1, 0), Point(1, 1), Point(0, 1)])
+    print(square.name, square.corners.len, "corners, perimeter", perimeter(square))
+    print(square)
+
+    // a linked list: new(...) puts a value on the heap, free(...) gives it back
+    ptr[Node] head = null
+    for i in 0..3 {
+        head = new(Node(value: i, next: head))
+    }
+    n := head
+    while n != null {
+        print("node", n.value)
+        next := n.next
+        free(n)
+        n = next
+    }
+}