CheckWeight SE: Check for extrinsic length + proof size combined

[skunert]

Currently the CheckWeight SignedExtension was tracking the size of the proof and the extrinsic length separately. But in reality we need one more check that ensures we don't hit the PoV limit with both combined.

The rest of the logic remains unchanged. One scenario where the changes make a difference is when we enter this branch:

polkadot-sdk/substrate/frame/system/src/extensions/check_weight.rs

Lines 185 to 198 in f34d8e3

	match limit_per_class.reserved {
	// We are over the limit in reserved pool.
	Some(reserved) if per_class.any_gt(reserved) => {
	log::debug!(
	target: LOG_TARGET,
	"Total block weight is exceeded.",
	);
	return Err(InvalidTransaction::ExhaustsResources.into())
	},
	// There is either no limit in reserved pool (`None`),
	// or we are below the limit.
	_ => {},
	}

This was previously allowing to some extrinsics that is exceeding the block limit but are withing the reserved area of BlockWeights. This will now be caught by the later check I introduced. I think the new behaviour makes sense, since the proof size dimension is designed for parachains and they don't want to go over the limit and get rejected.

In the long run we should maybe get rid of RuntimeBlockLength alltogether, however that would require a deprecation process and can come at a later point.

[bkchr]

Thank you!