fix(tests): resolve cross-platform path separator on Windows in test_builder_resolution

[FREEqueenC]

Description

Fixes a path separator issue in test_builder_resolution_integrity when running offline validation tests on Windows environments.

Problem

On Windows, pathlib.Path objects stringify using backslashes (\). In test_builder_resolution.py line 60:

local_module_path = f"{str(rel_path).replace('/', '.')}.builder"