Add CSE guarded expression lift fuzzer

[prozacchiwawa]

Summary

• Add a generated CSE fuzzer that builds typed abstract stack expressions over f, r, c, sha256, arithmetic, if, equality, strlen, and l.
• Render the same target expression into nested if, let, let*, and assign contexts with repeated occurrences in conditions, branches, and bindings.
• Compare optimized and unoptimized CL23 execution on both guarded-valid and guard-false inputs to catch CSE lifting expressions above protective if checks.

Testing

• cargo test test_generated_cse_does_not_lift_past_guarding_if -- --nocapture