feat(hts): coexisting multi-version CodeSystems with version-aware co…

[smunini]

…mpose

Drop the column-level UNIQUE on code_systems.url (both SQLite and PG schemas) and replace it with a composite UNIQUE index on (url, version). Two CodeSystems sharing a canonical URL now coexist whenever they declare distinct version values, matching tx-ecosystem fixtures version/codesystem-version-1.json / -2.json (both ship id:"version", url http://hl7.org/fhir/test/CodeSystem/version, versions 1.0.0 and 1.2.0). Add an idempotent SQLite migration (migrate_code_systems_drop_url_unique) that rebuilds the table without the legacy constraint, plus a PG DO-block that drops any pre-existing UNIQUE (url) constraint.

Storage id is now <fhir-id>|<version> (or <fhir-id> when version absent) so per-(url, version) rows have stable, distinct PK values without colliding when fixtures reuse the FHIR id across versions. Concepts / hierarchy / properties / designations FK to that synthetic storage id, so each version owns its own normalized data.

resolve_code_system (both backends) now picks the highest version when no version parameter is supplied, exact-matches when a literal version is given, and supports tx-ecosystem version-pattern syntax (1.x.x, 1.x, bare 1) — each x segment is a wildcard, bare numeric prefixes match any version starting with that segment, and the highest matching version wins.

Compose includes that pin a version (compose.include[].version) now resolve to the matching code_systems row instead of arbitrarily grabbing the first row by URL. The mixed value set tests/version/valueset-version-mixed.json (which pulls code1 from 1.0.0 and code2 from 1.2.0 of the same canonical URL) expands correctly. CRUD lookups by FHIR id (e.g. /CodeSystem/version) fall back to matching resource_json.id and pick the latest version when the synthetic storage id miss occurs. The hierarchy/concept-map helpers that look up system_id from a URL now ORDER BY version DESC LIMIT 1 so subsumption walks the most recent revision.

Targets the largest remaining tx-ecosystem bucket — the 147 failing version/ tests including coding-v10-vs1w, vs-expand-v1, code-vnn-* families, codeableconcept-v10-* and the mixed-version paths.

Adds 8 new unit tests covering: dual-version coexistence after import, exact / wildcard / short-prefix / unknown-version lookup, and three compose-version pinning scenarios (pin v1, pin v2, mixed). Updates the existing cs_create_indexes_into_hts_tables and
cs_delete_removes_hts_normalized_rows tests to match by URL rather than the now-synthetic storage id.

cargo test -p helios-hts --lib: 473 passed, 0 failed