TODO.md: add performance, tooling, and embedded features

add future work items:
- method inline caching improvements
- built-in profiler/benchmarking tools
- improved REPL (mirb) features
- configurable memory pools
- suspend/resume VM state
- CMake build support

Co-authored-by: Claude <noreply@anthropic.com>

TODO.md

@@ -5,7 +5,13 @@
 - parser and code generator independent from `mrb_state` (picoruby?)
 - pattern matching (case/in syntax, array/hash patterns, guards, etc.)
 - iv/hash entry cache
+- method inline caching improvements (cache method lookup results)
 - more peephole optimization (if possible)
+- built-in profiler/benchmarking tools (memory, method calls, timing)
+- improved REPL (mirb) features (multi-line, syntax highlighting, completion)
+- configurable memory pools (per-object-type, memory-constrained devices)
+- suspend/resume VM state (serialize/deserialize for power cycling)
+- CMake build support (better IDE integration, standard C tooling)
 
 # Things to do (Things we need to consider)