sql.py: DbConn: Cache query results as a dict subset of the cursor's key attributes, so that additional attributes can easily be cached by adding them to the subset list

dicts.py: Added AttrsDictView

util.py: NamedTuple.__iter__(): Removed unnecessary **attrs param

sql.py: _query_lookup(): Fixed bug where params was cast to a tuple, even though it could also be a dict. index_cols(): Changed to use the connection-wide caching mechanism rather than its own custom cache.

util.py: NamedTuple: Made it usable as a hashable dict (with string keys) by adding iter() and getitem()

dicts.py: Added make_hashable()

sql.py: DbConn: Only cache exceptions for inserts since they are not idempotent, but an invalid insert will always be invalid. If a cached result in an exception, re-raise it in a separate method other than the constructor to ensure that the cursor object is still created, and that its query instance var is set.

sql.py: insert(): Cache insert queries by default. This works because any DuplicateKeyException, etc. would be cached as well. This saves many inserts for rows that we already know are in the database.

sql.py: DbConn.run_query(): Cache exceptions raised by queries as well

sql.py: DbConn.run_query(): When debug logging, label queries with their cache status (hit/miss/non-cacheable)