Fix subject-ID modular probing formula

[pavel-kirienko]

Summary

• update non-pinned subject-ID allocation to the reduced modular formula used by Cy
• preserve pinned-topic behavior
• add regression coverage for zero-eviction stability and uint64-wrapping divergence
• bump package version to 2.0.0.dev5

Validation

• .nox/test-3-12/bin/python -m pytest -q tests/test_topic.py tests/test_integration.py::test_subject_id_computation
• nox -s test-3.12 mypy lint format --force-python 3.12

Note: full default nox also attempted locally, but Python 3.11 and 3.13 interpreters are not installed on this host.