fixes various incompatabilities with current versions

[MatthiasWinkelmann]

This now works for me, with crystal 1.2.2 on macOS Monterey (ARM64), if anyone cares.

I'm not entirely sure if what it's measuring is the so-called "reality". Specifically, the in-memory store is three orders of mag faster for me than redis (1450x, see below). There may be some compiler optimizations going on that completely bypass the work for that implementation.

|                  | set      | get      | get(empty) | delete   |
| ---------------- | -------- | -------- | ---------- | -------- |
| **MemoryStore**  | 16871250 | 30060000 |   29883750 | 20672500 |
| **LevelDBStore** |    12500 |   441250 |     437500 |    50000 |
| **RedisStore**   |    11250 |    11250 |      11250 |     6250 |
| **FileStore**    |     4000 |    18750 |      18750 |    87500 |