Add debug.log and debug.assert statements

Parser:
- debug.log(expr, ...) and debug.assert(cond) syntax
- parse_debug_statement() handles both methods
- New AST variants: Statement::DebugLog and Statement::DebugAssert

Codegen:
- CodeGen::with_debug(bool) to toggle debug instrumentation
- DebugLog writes each expression to $4800 (Mesen debug port)
- DebugAssert evaluates condition; on false, writes $FF to $4800 + BRK
- Both are stripped entirely when debug_mode = false (release builds)

CLI:
- --debug flag now wired through to CodeGen
- Without --debug, all debug statements produce zero bytes

Analyzer:
- Type-checks DebugAssert condition as bool
- Walks DebugLog args for reads (used_vars tracking)

IR lowering:
- DebugLog/DebugAssert are no-ops (codegen handles them directly)

254 tests (5 new: 3 parser + 2 codegen).

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

src/analyzer/mod.rs

@@ -606,6 +606,15 @@ impl Analyzer {
             | Statement::Return(None, _)
             | Statement::LoadBackground(_, _)
             | Statement::SetPalette(_, _) => {}
+            Statement::DebugLog(args, _) => {
+                for arg in args {
+                    self.walk_expr_reads(arg);
+                }
+            }
+            Statement::DebugAssert(cond, _) => {
+                self.walk_expr_reads(cond);
+                self.check_expr_type(cond, &NesType::Bool);
+            }
         }
     }
 
@@ -804,6 +813,14 @@ fn collect_calls_stmt(stmt: &Statement, calls: &mut Vec<String>) {
             collect_calls_expr(x, calls);
             collect_calls_expr(y, calls);
         }
+        Statement::DebugLog(args, _) => {
+            for arg in args {
+                collect_calls_expr(arg, calls);
+            }
+        }
+        Statement::DebugAssert(cond, _) => {
+            collect_calls_expr(cond, calls);
+        }
         Statement::Return(None, _)
         | Statement::Transition(_, _)
         | Statement::WaitFrame(_)