Add source-only Armenia Axiom integration

[MaxGhenis]

Scope

Add a source-only Armenia integration behind the policyengine.py interface. The integration must execute RuleSpec through the real Axiom runtime and preserve Microcosm household-weight inheritance.

Acceptance criteria

• Add AMYearData and PopulaceArmeniaDataset without registering or downloading an uncertified population.
• Require a content-addressed Microcosm release manifest and verify the supplied H5 before loading it.
• Add an Axiom-backed Armenia model identity and execution receipt.
• Require cryptographically verified Axiom encoder apply manifests for RuleSpec inputs.
• Register PolicyEngine variables from Axiom's derived-variable metadata.
• Reject PolicyEngine policy dictionaries and behavioral overlays; counterfactuals require a separately signed RuleSpec artifact.
• Exercise executable behavior only through the real Axiom runtime. Tests skip when the native source stack is unavailable.

Non-goals

This work does not certify an Armenian population, establish current-law completeness, publish national results, or implement Armenian tax-benefit rules in Python.