M2: Add call graph analysis, recursion detection, and optimizer

Analyzer extensions:
- Call graph construction from function bodies and state handlers
- DFS-based recursion detection (direct and mutual) with E0402 errors
- Max call depth computation per entry point with E0401 enforcement
- Function declarations registered as symbols (E0503 for undefined calls)
- Collects calls from all statement/expression types recursively

Optimizer (new module):
- Constant folding: evaluate known-constant arithmetic at compile time
- Dead code elimination: remove ops with unused destination temps
- Both operate per-basic-block in a single pass

171 tests total (22 new: 6 analyzer + 11 IR lowering + 5 optimizer)

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

src/lib.rs

@@ -2,8 +2,10 @@ pub mod analyzer;
 pub mod asm;
 pub mod codegen;
 pub mod errors;
+pub mod ir;
 pub mod lexer;
 pub mod linker;
+pub mod optimizer;
 pub mod parser;
 pub mod rom;
 pub mod runtime;