Introduce a function for easy Extrinsic decoding of Block

[haerdib]

With #541 we decode blocks with OpaqueExtrinsic. As this is not human readable, it would be nice for the users to still have a convenient function to decode the block / extrsinic.

See also the config:

substrate-api-client/primitives/src/config/asset_runtime_config.rs

Line 35 in 53be73d

type Block = Block<Self::Header, OpaqueExtrinsic>;

I see two solutions for this:

1. Design a helper function that lets the user decode an Opaque Extrinsic (input) into a self defined Extrinsic (generic input).
2. A getter generic getter function, that expects an Extrinsic Type input. Something like this

fn get_signed_runtime_block<Extrinsic: DeserializeOwned>(&self, hash: Option<Hash>) {
    let block_type = ac_primitives::Block<config::Header, Extrinsic>;
     ....
}

Where the user could define the block type with Runtime::RuntimeBlock. Or a convenience function where a Vec of OpaqueExtrinsic gets decoded to a Vec of "real" extrinsic.

Examples for making it clear what's the difference between Opaque and not:
RuntimeBlock:

Some(Block { header: Header { parent_hash: 0xd80617a625261c16d705a3dac9acfd59906e8c2e12a3e8b595e2a8d284b43606, number: 3, state_root: 0x0d16fa7598d4b802c357b90815b82692d0acc84216896f06cff459b793ba8862, extrinsics_root: 0x1f0210efea3486f0c2452bc87b511a127d055f4ddb825d83c54ed040920ff1a7, digest: Digest { logs: [DigestItem::PreRuntime([66, 65, 66, 69], [1, 0, 0, 0, 0, 58, 155, 110, 33, 0, 0, 0, 0, 248, 194, 255, 172, 156, 240, 170, 13, 11, 179, 186, 106, 94, 193, 229, 233, 175, 119, 218, 242, 176, 184, 137, 139, 53, 173, 150, 248, 34, 63, 120, 6, 207, 45, 204, 81, 189, 224, 4, 244, 19, 248, 62, 187, 55, 63, 165, 186, 14, 121, 212, 210, 45, 87, 144, 231, 141, 2, 43, 90, 171, 238, 67, 12, 213, 98, 162, 82, 97, 67, 193, 166, 105, 209, 13, 68, 164, 51, 216, 164, 7, 157, 197, 12, 240, 107, 31, 184, 28, 177, 121, 125, 71, 230, 212, 12]), DigestItem::Seal([66, 65, 66, 69], [142, 123, 71, 63, 12, 254, 31, 33, 132, 40, 175, 199, 98, 102, 126, 150, 13, 4, 20, 181, 175, 103, 111, 128, 147, 185, 42, 151, 64, 177, 202, 28, 115, 128, 195, 231, 212, 47, 32, 165, 37, 237, 250, 120, 141, 147, 15, 168, 27, 94, 117, 252, 205, 109, 77, 124, 147, 22, 233, 60, 60, 43, 127, 139])] } }, extrinsics: [UncheckedExtrinsic(None, RuntimeCall::Timestamp(Call::set { now: 1682690478001 }))] }) 

Opaque Extrinsic Block:

Some(SubstrateBlock { header: SubstrateHeader { parent_hash: 0xcf7dcf0e87422167a4fc033dc77fa5c6a6c3e73d4ac451b56f150dd6b3afe7e8, number: 2, state_root: 0xd1af5a7496757c79d7c64ece5dc5cad5a2f35d9e677113e1a8e412607f228b9b, extrinsics_root: 0x9c52e3c8b4b6fce5852d35b58e3a01bf5f52b2538aa543a0dd4b001445f62fc8, digest: Digest { logs: [PreRuntime([66, 65, 66, 69], [1, 0, 0, 0, 0, 162, 84, 112, 33, 0, 0, 0, 0, 172, 245, 187, 4, 171, 140, 237, 185, 227, 230, 1, 154, 239, 137, 177, 75, 63, 65, 92, 105, 165, 138, 96, 114, 45, 190, 225, 197, 130, 82, 219, 119, 143, 50, 209, 253, 104, 177, 130, 147, 90, 113, 187, 91, 188, 27, 46, 162, 176, 112, 122, 241, 142, 220, 216, 38, 177, 200, 1, 151, 63, 125, 11, 9, 165, 178, 165, 1, 109, 248, 134, 156, 171, 122, 155, 123, 208, 181, 189, 172, 169, 164, 112, 90, 226, 59, 65, 4, 159, 206, 15, 27, 33, 45, 91, 10]), Seal([66, 65, 66, 69], [74, 199, 233, 119, 144, 50, 95, 196, 248, 112, 81, 52, 94, 221, 229, 203, 33, 176, 34, 83, 91, 112, 131, 12, 71, 167, 176, 126, 11, 121, 128, 94, 107, 62, 186, 18, 151, 3, 226, 172, 248, 134, 71, 226, 102, 173, 61, 210, 140, 131, 82, 105, 169, 38, 7, 125, 15, 23, 152, 96, 116, 14, 94, 136])] } }, extrinsics: [SubstrateOpaqueExtrinsic([4, 3, 0, 11, 112, 202, 95, 220, 135, 1])] })