The idea is that in future tokens will encode a mapping of instance to position. However, we don't want to include the full instance name in the string representation, so instead we'll have a mapping between instance name and an immutable integer ID in the DB that we can use instead. We'll then do the lookup when we serialize/deserialize the token (we could alternatively pass around an `Instance` type that includes both the name and ID, but that turns out to be a lot more invasive).
This removes `SourcePaginationConfig` and `get_pagination_rows`. The reasoning behind this is that these generic classes/functions erased the types of the IDs it used (i.e. instead of passing around `StreamToken` it'd pass in e.g. `token.room_key`, which don't have uniform types).
Python will return a tuple whether there are parentheses around the returned values or not.
I'm just sick of my editor complaining about this all over the place :)
parse_integer and parse_string can take a request and raise errors
in case we have wrong or missing params.
This PR tries to use them more to deduplicate some code and make it
better readable
