feat: add drop key functionality (#6)

Currently, the `Table.Drop()` function is deprecated because it is not implemented yet. Let's add that functionality.

- Adds true drop functionality to the table, through `Table.Drop()`.
- Adds tests for functionality.
- Rewrites fuzz test using `go_fuzz_utils`, to test arbitrary usage patterns.
- Rewrite `bucket` to allow a capacity of zero.
- Rename `Table.Capacity()` to `Table.TotalCapacity()`, to reflect to different between the capacity of the buckets vs. the whole table.
- Enforce 100% mutation test coverage.

Reviewed-on: #6
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

cuckoo_internal_test.go

@@ -25,6 +25,6 @@ func TestLoad(t *testing.T) {
 	for i := range 16 {
 		err := table.Put(i, true)
 		assert.NoError(err)
-		assert.Equal(float64(table.Size())/float64(table.Capacity()), table.load())
+		assert.Equal(float64(table.Size())/float64(table.TotalCapacity()), table.load())
 	}
 }