Feasibility review for addition of duckdb backend

[gkennos]

• confirm SQLAlchemy interface support to review if current API meets all existing backend requirements
• performance testing to assess prioritisation of addition of new backend support

[gkennos]

@nicoloesch in conversation with @ivcvy, we proposed following the omop-emb structure of treating duckdb as a 2nd tier interface for read only - interested if you have thoughts