test(mir): fix test compilation after Call instruction callee field addition

Fixes test compilation errors caused by adding callee: Option<Callee> field
to MirInstruction::Call in previous commits.

Changes:
- tests/mir_instruction_unit.rs:
  - Add callee: None to all Call instruction constructions
  - Ensures backward compatibility with existing tests

- src/mir/instruction/tests.rs:
  - Add callee: None to Call instruction in phi_merge_if test
  - Maintains test correctness after Call signature change

- src/mir/value_id.rs:
  - Add ValueId::INVALID constant (u32::MAX)
  - Provides clear sentinel value for invalid/placeholder IDs

- src/mir/phi_core/loopform_builder.rs:
  - Replace deprecated ValueId::from() with ValueId::new()
  - Replace deprecated BasicBlockId::from() with BasicBlockId::new()
  - Ensures consistency with updated ID construction patterns

Test Status:
- Original errors from our commit: 6 → 0 ✅
- Remaining errors: 45 (pre-existing, unrelated to our changes)
  - 14: Missing interpreter module (legacy)
  - 11: Missing VM in backend::vm (moved)
  - 7: Missing jit module (archived)
  - 5: Missing MirInterpreter methods (legacy)
  - 4: Missing Box operator methods (pre-existing)

All test errors related to LocalSSA and Call instruction changes are resolved.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/mir_instruction_unit.rs

@@ -37,6 +37,7 @@ fn test_call_instruction() {
     let inst = MirInstruction::Call {
         dst: Some(dst),
         func,
+        callee: None,  // Legacy mode for test
         args: vec![arg1, arg2],
         effects: EffectMask::IO,
     };