Fix unfindable entry in sparsemap

[Nycto]

A few changes contained here:

1. Fixes a bug in the bundled sparsemap implementation that was preventing some entries from being located.
2. Adds a bulk operations test that runs the map through a long list of operations
3. Moves sparsemap.nim into a util directory
4. Adds github actions for specifically testing with the various memory profiling modes enabled.

[Nycto]

@ninovanhooff Any other concerns here?

[ninovanhooff]

@Nycto nope, go ahead