Fix for benchmarking nits

[bkontur]

This PR contains benchmarking nits and fixes.

• For Polkadot and pallet_bags_list where benchmarks fails for AutoRebagNumber = 0 (https://github.com/polkadot-fellows/runtimes/actions/runs/17017979638/job/48243408516)
  • possibly we could also fix the benchmark itself
• Probably funds and KeyDeposit related https://github.com/polkadot-fellows/runtimes/actions/runs/16988940719/job/48163751298

The following 3 benchmarks failed:
- pallet_session::purge_keys
- pallet_session::set_keys
- runtime_parachains::disputes::slashing::report_dispute_lost_unsigned
Error: Input("3 benchmarks failed")

• promote_fast - rewrites u16 to u32 which does not compile
  • probably needs polkadot-sdk fix (need to investigate and create polkadot-sdk issue)

• Does not require a CHANGELOG entry

[kianenigma]

About key deposit, we agreed elsewhere to set it to 0.

Can you also adjust this line in the release note to:

Setting session keys now might charge a storage deposit. The amount can be inspected in the Session::KeyDeposit of the runtime metadata. This value is intended to be set post AHM. Validators should make sure they have some free balance to cover this deposit the next time they want to rotate their keys.

[ggwpez]

We can make this controllable by the rc-migrator pallet that will automatically enable it after the migration.
Will do when its possible.