Replace LimitedSizeDict with cachetools

[Dunedan]

When receiving game reports from Pyrogenesis, it regularly happens that we never receive a report from both players of a rated game. This happens in the following situations:

1. One of the player rage-quits by force-closing Pyrogenesis.
2. One player looses lobby connectivity during the game.
3. The rated game has only one human player and the other player is a bot (while Pyrogenesis shouldn't send reports for such games, here we are right now).

As we cache game reports in memory until we received and compared them from both players of a rated game, this means that the LimitedSizeDict used for that would reach its maximum size of 4096 items pretty fast. While that doesn't impact functionality, it's using up way more memory than necessary.

Additionally EcheLOn contained a bug which wouldn't even remove games from the LimitedSizeDict, where we did receive all reports for.

While we can (and actually do in this commit) fix the bug in EcheLOn, we have no control over the situations where we don't receive reports from both players. However, what we can do is to remove reports for games where we're pretty certain, that we'll never receive the missing report anymore.

To do so, this commit replaces the custom LimitedSizeDict class with a dependency on cachetools. For tracking reports from rated games a size-limited TTLCache is now used which evicts reports belonging to games after 1 hour, as we don't expect to receive reports later than a few seconds after the end of a rated game.

This should result in a significant reduction of the memory required by EcheLOn.