OMOP samples

[ofermend]

What this adds

• A new OMOP sample showing how to analyze observational health data in the OMOP Common Data Model using Malloy. OMOP is the dominant open standard (maintained by OHDSI) for standardizing electronic health records, used across hundreds of academic medical centers and research networks. The sample is built around a generic semantic model (omop.malloy) that conforms to OMOP CDM v5.3 and v5.4.
• We use here the synthea-covid19-10k dataset (~10,700 synthetic patients, OMOP CDM v5.3) which uses Synthetic data (no PHI).

The model captures some OMOP-specific querying challenges Malloy handles well:

• Symmetric aggregates: counting conditions, drugs, visits, and procedures per patient in one query without fan-out errors.
• Reusable vocabulary joins: the concept dictionary reused under plain-English aliases (gender, drug_concept, condition_concept, race, ethnicity) so queries ask for readable names instead of numeric codes.
• Named views: cohort logic and demographic breakdowns defined once and reused across analyses.

The specific dataset has no laboratory results (measurement/observation tables are empty) and unpopulated drug dosing fields, so lab/vital and prescription-length analyses are out of scope. Noted in the README.