M2: Add function/array parsing, IR data structures and lowering

Parser extensions:
- Function declarations with params and return types (fun, inline fun)
- Array type syntax (u8[16]), array literal expressions ([1, 2, 3])
- fast/slow variable placement hints
- Functions stored in Program AST

IR module (new):
- IrProgram, IrFunction, IrBasicBlock, IrOp, IrTerminator types
- AST-to-IR lowering pass with:
  - Expression lowering to virtual temps
  - Control flow (if/else, while, loop) to basic blocks with branches
  - Break/continue via loop context stack
  - Short-circuit logical and/or
  - Button reads, draw sprites, wait_frame
  - Constants inlined as LoadImm
  - State handlers lowered as separate IR functions

Tests: 6 new parser tests, 11 new IR lowering tests (153 total)

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

src/parser/ast.rs

@@ -76,9 +76,7 @@ pub struct ConstDecl {
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Placement {
-    #[allow(dead_code)]
     Fast,
-    #[allow(dead_code)]
     Slow,
     Auto,
 }
@@ -89,7 +87,6 @@ pub enum NesType {
     I8,
     U16,
     Bool,
-    #[allow(dead_code)]
     Array(Box<NesType>, u16),
 }
 
@@ -121,6 +118,7 @@ pub enum Expr {
     UnaryOp(UnaryOp, Box<Expr>, Span),
     Call(String, Vec<Expr>, Span),
     ButtonRead(Option<Player>, String, Span),
+    ArrayLiteral(Vec<Expr>, Span),
 }
 
 impl Expr {
@@ -133,7 +131,8 @@ impl Expr {
             | Self::BinaryOp(_, _, _, s)
             | Self::UnaryOp(_, _, s)
             | Self::Call(_, _, s)
-            | Self::ButtonRead(_, _, s) => *s,
+            | Self::ButtonRead(_, _, s)
+            | Self::ArrayLiteral(_, s) => *s,
         }
     }
 }