on_idle deregistration logic for SN0

[Supremesource]

How does on_idle work?

• https://github.com/paritytech/polkadot-sdk/blob/ad8620922bd7c0477b25c7dfd6fc233641cb27ae/bridges/modules/messages/src/lib.rs#L194
• https://crates.parity.io/frame_support/pallet_prelude/trait.Hooks.html#method.on_idle

What needs to be done?
Since we need to work with weight info:

• Benchmark our on_initialize logic
  • See: https://github.com/paritytech/polkadot-sdk/blob/ad8620922bd7c0477b25c7dfd6fc233641cb27ae/bridges/modules/parachains/src/benchmarking.rs#L45

How will the deregistering me handeled:

• Free block weight: Run our on_idle deregistration logic
• Create a function called deregister_unwhitelisted
  • This function takes the whitelist that is working on sn0 and deregisters ~1-5 modules that are not in the whitelist until there aren't any modules left outside of the whitelist.

Notes: work with subnet id (netuid) 0. We always get the modules, and perform the deregistrations only there. This is not affecting any other subnet.
For further context, you can read
https://discord.com/channels/941362322000203776/1105911230461394964/1245740345564729475