Enable remote SQLite references

This is now or soon possible with updates to the duckdb SQLite extension, see here for more: https://github.com/duckdb/duckdb-sqlite/issues/39 . In the long run, this may be more efficient than caching local copies for queries on remote datasets.

Start by reading the linked duckdb-sqlite issue 39 and determine whether the required remote-reference support is available. Then inspect CytoTable's current handling of cached local copies and define how remote SQLite datasets should be queried; done means remote SQLite references work without requiring local caching.

Written by the indexing model from the issue text.