[CONNECT] Apply database schema already when connecting

At [^1] and [^2], we have been using SQLAlchemy's abilities to specify the database schema on the connection string already, using `?schema=foobar`. In this way, table names will not need to be addressed in full-qualified notation "by hand". Instead, they can be addressed by using basename only, when selecting the schema at connection time already.

Let's also do it in the same spirit here.

[^1]: https://github.com/crate-workbench/mlflow-cratedb
[^2]: https://github.com/crate-workbench/langchain

No source files or tests are named. Start at the connection-string handling for the CONNECT path and inspect how SQLAlchemy URL query parameters are applied; compare the linked mlflow-cratedb and langchain integrations. Done means `?schema=foobar` selects the requested schema so table references can use basenames rather than fully qualified names.

Written by the indexing model from the issue text.