conformance: add runnable AKN4OLF conformance suite

[Sipioteo]

Summary

The spec README points to ./conformance and calls the conformance suite "the heart of the project … the only gate", but that directory did not exist (the link 404'd). This PR adds the real, runnable suite.

A new conformance/ package implements the six criteria from the README as a dependency-free Python library + CLI (standard library only — xml.etree.ElementTree), so any adapter author can run it.

What's included

• conformance/akn4olf_conformance.py — library + CLI implementing criteria 1–6.
• conformance/__init__.py — public API: check(), stability(), report types.
• conformance/README.md — per-criterion definitions, what is mechanically enforced vs advisory, how to run.
• conformance/samples/ — a real Normattiva conformant sample (single-version), a synthetic multi-version conformant sample, and a deliberately non-conformant sample.
• conformance/selftest.py — self-test over the bundled samples.
• Top-level README.md — the ./conformance link now resolves; added a short pointer with run commands.

The six criteria

1. Schema-valid Akoma Ntoso in a recognized profile — well-formed XML; {akn}akomaNtoso root; one recognized document element (act/bill/doc/…) with {akn}meta; the OLF proprietary source="#openlawsfoundation" agent IDREF resolves to a declared TLCOrganization. Structural by default and labelled as such; validates against an offline AKN XSD if one is provided via AKN4OLF_XSD (with lxml). No official XSD is bundled.
2. Required lifecycle events present and well-formed — <olf:lifecycle> with a valid ISO inForceFrom; events drawn from the fixed vocabulary {enacted, published, commenced, amended, repealed} with valid dates. The README does not enumerate the mandatory set in prose, so the suite adopts a minimal, stated interpretation (require inForceFrom + a matching commenced) documented in code and the README.
3. Every <ref> resolved-or-unresolved — each {akn}ref carries either a well-formed {olf}target OLF id or {olf}resolution="unresolved"; reports counts.
4. Temporal validity monotonic — distinguishes the act-level OLF envelope (checked for internal consistency) from native <temporalGroup> version slices (which must be pairwise non-overlapping and contained in the envelope).
5. As-enacted text reconstructible — only meaningful for multi-version documents; returns NOT-APPLICABLE (not a false PASS) for single-version monovigente inputs.
6. OLF identifiers stable across regenerations — a two-input check comparing identity, ref-target ids, and structural eIds while ignoring volatile provenance; run via --compare or stability().

NOT-APPLICABLE criteria are surfaced but never make a document non-conformant.

How to run

python -m conformance.akn4olf_conformance path/to/document.akn.xml
python -m conformance.akn4olf_conformance run1.akn.xml --compare run2.akn.xml
python -m conformance.selftest

The CLI exits 0 on CONFORMANT (and stability PASS) and 1 otherwise, for direct CI use.

Validation

• Real conformant sample → CONFORMANT (criterion 5 NOT-APPLICABLE, correct for a monovigente snapshot).
• Synthetic multi-version sample → CONFORMANT (criteria 4 and 5 PASS).
• Non-conformant sample → NON-CONFORMANT, naming criterion 3 as the cause.
• Stability: two regenerations from the same source (different generation timestamps) → PASS; a copy with a changed id → FAIL.
• python -m conformance.selftest → all assertions hold.

Honest limitations (documented in conformance/README.md)

• No official AKN 3.0 XSD is redistributed here; criterion 1 is structural unless an XSD is supplied offline.
• Criterion 5 needs a multi-version document; it is NOT-APPLICABLE for single-version inputs.
• Criterion 6 needs two regenerations (--compare).