Add `ProofSizeExt` to benchmarks (#5257)

I propose to have `ProofSizeExt` available during benchmarking so we can
improve the accuracy for extensions using it.

Another thing we could do is to also enable recording for the timing
benchmark here:

https://github.com/paritytech/polkadot-sdk/blob/035211d7/substrate/utils/frame/benchmarking-cli/src/pallet/command.rs#L232

Parachains will need to have recording enabled during import for
reclaim, so we could enable it here and provide a flag
`--disable-proof-recording` for scenarios where one does not want it.
Happy to hear opinions about this.