Feature/ibis execution api

[egillax]

Implements an experimental native Ibis execution API for Circepy with lazy relation building and
explicit materialization actions.

• Adds IbisExecutor with build(), to_pandas(), to_polars(), and write() methods
• Adds convenience wrappers: build_ibis, to_polars, write_cohort
• Introduces ExecutionOptions for execution/schema/materialization/SQL-capture controls
• Ports and simplifies executor logic from Mitos into Circepy where I used like a registry-based factory
• Adds tests for API behavior and write-option validation
• Validated DuckDB parity against CirceR row counts across phenotype-library cohorts (local integration
  run)

Sorry for how large this is. The API is in circe/execution/ibis.py

There is some stuff in there I'm not completely satisifed with, but good enough for you to have a look @azimov