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>

tests/run/modules.fn

@@ -0,0 +1,18 @@
+import geometry
+import shapes
+
+fn main() {
+    v := geometry.Vec(3, 4)
+    print(geometry.length(v))
+    w := geometry.add(v, geometry.Vec(x: 1, y: 1))
+    print(geometry.describe(w))
+    geometry.Vec z
+    print(z)
+    b := shapes.Box(size: geometry.Vec(2, 5))
+    print(shapes.area(b), b)
+    total := 0
+    for i in 0..3 {
+        total += i
+    }
+    print("total", total)
+}