Make import_module_from_file resolve relative paths consistently with exec_file #7

Currently, exec_file resolves relative paths against the testbench directory using the shared VUnit runner state, while import_module_from_file passes its path directly to Python, resolving relative paths against the simulator’s working directory.

This makes importing Python models from verification components unnecessarily awkward: the component must receive an absolute path or obtain the testbench path explicitly.

Please make both APIs use the same path resolution:

• Resolve relative paths against the top-level testbench directory.
• Preserve absolute paths unchanged.
• Allow calls from verification components and VHDL package procedures without passing tb_path or runner_cfg locally.

For example, after test_runner_setup, a component should be able to write:

import_module_from_file("models/filter.py", "filter_model");
result := call_integer("filter_model.compute", arg(21));

This should load models/filter.py relative to the top-level testbench directory.

The existing p_file_path helper used by exec_file could be shared with import_module_from_file.

Acceptance criteria:

• Relative imports work from a child component after runner setup, even when the simulator’s working directory differs from the testbench directory.
• Absolute paths and the optional session parameter retain their existing behavior.
• import_run_script, which uses import_module_from_file internally, continues to work.
• Documentation explains the path base and runner-setup requirement.
• Release notes flag the change for callers relying on working-directory-relative imports.

Resolving paths relative to the calling component’s own VHDL source directory is outside the scope of this issue.