Rework `on_ready` function

[ctmbl]

• the on_ready function creates the COG, db maanger, api maanger and rate limiter
• but the documentation says this function xcan be called multiple times: https://discordpy.readthedocs.io/en/stable/api.html#discord.on_ready
• so maybe it could create 2 loops coexisting, but only one bot alive that could create these behaviors:

2024-04-12 21:28:23 ERROR    api.rate_limiter Entering idle state due to previous errors
2024-04-12 21:28:43 ERROR    api.rate_limiter Entering idle state due to previous errors

it has to be reworked