update maps/slice imports and use slog

[plastikfan]

Version 1.21.3 now includes maps and slices as standard. The current imports:

import (
    "golang.org/x/exp/maps"
    "golang.org/x/exp/slices"
)

... need to be updated to not use the experimental versions

Replace zap with slog

[plastikfan]

strange thing is, there is now no Keys function on maps, so now reverting to use lo.Keys instead, which really shouldn't be necessary.