Complete Phase 8.5A: MIR 25-instruction hierarchical implementation with working tests and demo

Co-authored-by: moe-charm <217100418+moe-charm@users.noreply.github.com>

src/mir/builder.rs

@@ -354,7 +354,7 @@ impl MirBuilder {
         // For now, use a special Print instruction (minimal scope)
         self.emit_instruction(MirInstruction::Print {
             value,
-            effects: EffectMask::PURE.add(Effect::IO),
+            effects: EffectMask::PURE.add(Effect::Io),
         })?;
         
         // Return the value that was printed