Remove hardcoded /tmp/bindings.py path in test_static_demo.py

[coderabbitai]

Summary

The test fixture decl in numbast/src/numbast/experimental/mlir/static/tests/test_static_demo.py writes generated binding source to the fixed absolute path /tmp/bindings.py. This can cause collisions in parallel test runs and reduces portability across environments.

The path should be replaced with pytest's tmp_path fixture to ensure each test run uses an isolated temporary directory.

References

• Flagged in PR Migrate experimental MLIR backend #346 (comment: Migrate experimental MLIR backend #346 (comment))
• Requested by @isVoid

Acceptance Criteria

• Replace the hardcoded /tmp/bindings.py path with a tmp_path-based path in the decl fixture.
• Verify no other occurrences of /tmp/bindings.py exist in the test file that need updating.