Provide more informative error messages if the input for SqlImplementation is not a valid sqlite file

currently if we pass in something invalid to SqlImplementation, it will not complain until *after* an operation is performed, rather than at connection/instantiation time

furthermore, the stack trace from sql aclhemy can be confusing - see #212

we should fail early with bad SqlImplementation connections (and with implementations in general)

Locate the SqlImplementation entry point and reproduce how an invalid SQLite input is accepted until an operation runs. Inspect the existing connection and implementation tests, then verify that invalid inputs fail during instantiation with an informative error rather than a confusing SQLAlchemy traceback.

Written by the indexing model from the issue text.