Some massive changes to make flakiness better

Renamed the @inputs to @top. This was a misguided attempt to make a
different change, but it's going to stick, now.
Began moving packages to their own folder rather than being intermingled
with overlays
Created a local overlay that just includes my personal packages
Cleaned up some dead code
Moved to just using the raw 'imports' instead of needing to explicitly
call out the `foo = import foo.nix {};` syntax

checks.nix

@@ -8,6 +8,7 @@
       # Needs https://github.com/DeterminateSystems/flake-checker/pull/130
       #flake-checker.enable = true;
       nixfmt-rfc-style.enable = true;
+      check-merge-conflicts.enable = true;
     };
   };
 }