Posetta Stone v0.1.0

Initial packaged release of Posetta Stone.
Includes the posetta_stone Python package namespace, the packaged PyO3 Rust extension, finite-poset analysis utilities, incidence algebra models, canonical family constructors, backend status/override helpers, and Python fallback paths for policy-disabled Rust operations.
Validated with the Python test suite, Rust test suite, release wheel build, and fresh virtualenv import check.