Fix broken pallet_shards benchmarks

[4meta5]

Closes #1016

shards pallet fixes

• split UnexpectedCommit error into each possible error branch, 2 branches: (1) return UnexpectedCommit error iff commit is not expected to be called because of the member's current status not equalling MemberStatusAdded (2) return MemberPeerIdNotFound error iff the member has not been registered via the members pallet prior to calling commit
• replaced non-generic pallet_shards::Config direct inheritance requirements with generic requirements that match all other custom pallets: frame_system::Config<AccountId = AccountId> + pallet_balances::Config<Balance = Balance>

All of these changes were required by the benchmarking fixes in this PR (listed further below).

shards pallet unit test fixes

• impl pallet_members::Config for pallet_shards::mock::Test
• configure new Members instance as Members config for pallet_shards::mock::Test impl of pallet_shards::Config
• update all pallet-shards unit tests s.t. they pass after the above changes to pallet_shards::mock (requires registering member prior to every call to commit)

shards pallet benchmarking fixes

• commit
• ready

[haider-rs]

seems to give a compilation error after geenrating weights:

use polkadot_sdk::*;

any idea why this import was removed from the weight.rs file?

[4meta5]

@penumbra23 do you know why the import was removed when the weight machine pushed the weights?

[haider-rs]

looking good!