Small refactorings between core and handler

[SammyWhamy]

Currently core contains some functions that should not be there:

src/redis.ts - checkRedis

This function should be refactored into something like

type cooldownCheckResult = { canUse: true } | { canUse: false, canUseAt: number };

async function checkCommandCooldown(key: string, cooldown: number, userId: string): Promise<cooldownCheckResult> {
    // If key doesnt exist, set the key+ttl, return { canUse: true }
    // If the key does exist, return { canUse: false,  canUseAt: ... }
}

This function should also be moved to handler, as it is only used for commands.

src/redis.ts - setExpireCommand

This function can probably removed, and we can simply set the TTL, or override it.
If it is necessary to not reset the ttl, we can change this to setexNoReset or something similar, and the logging can be removed.
This can be kept in core without the logging (or changed logging to be more generic).

src/redis.ts - handleExpiration

This function should be named instead like handlerComponentExpiry, and should be moved to handler, as it will be only used there.