rewrite decay

[hburn7]

Closes #87, #85

Changes:

• Fixed bug where decay would not begin at the correct time.
• Fixed issue where the initial rating adjustment was set to a very old default time. Now, it is set to the time of the first match's start time minus one second.
• Fixed issue where initial rating adjustments for rulesets were created even though players had no matches for that ruleset.
• Refactored the decay codebase to be more robust and testable
• Fixed bug where players would see no real-time inactivity decay
• Removed unused crates
• Added more processing print statements
• Changed DECAY_DAYS to 121

Screenshots:

No initial rating for other rulesets:

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Decay now extends to present time (Vaxei):

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