general: initial flake8 checks (for now manual)

fix fairly uncontroversial stuff in my.core like
- line spacing, which isn't too annoying (e.g. unlike many inline whitespace checks that break vertical formatting)
- unused imports/variables
- too broad except

my/core/influxdb.py

@@ -38,6 +38,7 @@ def fill(it: Iterable[Any], *, measurement: str, reset: bool=RESET_DEFAULT, dt_c
 
     # TODO need to take schema here...
     cache: Dict[str, bool] = {}
+
     def good(f, v) -> bool:
         c = cache.get(f)
         if c is not None:
@@ -79,7 +80,6 @@ def fill(it: Iterable[Any], *, measurement: str, reset: bool=RESET_DEFAULT, dt_c
                 fields=fields,
             )
 
-
     from more_itertools import chunked
     # "The optimal batch size is 5000 lines of line protocol."
     # some chunking is def necessary, otherwise it fails