Use Runtime APIs instead of RPCs

[gregdhill]

The latest subxt release (v0.29.0) includes support for metadata v15 and generating a runtime API interface. See this PR for more detail on how to consume the new (unstable) interface. We can replace any existing RPC calls (.rpc().request("xxx")) with the generated code and presumably use the static metadata for types such as BalanceWrapper.

[nakul1010]

The interbtc substrate dependencies needs to be upgraded to v1.0.0 release to generate the v15 metadata that can be decoded by subxt.

[nakul1010]

subxt cli command to generate metadata
subxt metadata --version unstable -f bytes > metadata-parachain-kintsugi.scale

Error received

Error: 
   0: Could not decode `RuntimeMetadataPrefixed.1`:
   0:     Could not decode `RuntimeMetadata::V15.0`:
   0:         Could not decode `RuntimeMetadataV15::extrinsic`:
   0:             Could not decode `ExtrinsicMetadata::extra_ty`:
   0:                 Could not decode `UntrackedSymbol::id`:
   0:                     out of range decoding Compact<u32>
   0: 
   1: Could not decode `RuntimeMetadata::V15.0`:
   1:     Could not decode `RuntimeMetadataV15::extrinsic`:
   1:         Could not decode `ExtrinsicMetadata::extra_ty`:
   1:             Could not decode `UntrackedSymbol::id`:
   1:                 out of range decoding Compact<u32>
   1: 
   2: Could not decode `RuntimeMetadataV15::extrinsic`:
   2:     Could not decode `ExtrinsicMetadata::extra_ty`:
   2:         Could not decode `UntrackedSymbol::id`:
   2:             out of range decoding Compact<u32>
   2: 
   3: Could not decode `ExtrinsicMetadata::extra_ty`:
   3:     Could not decode `UntrackedSymbol::id`:
   3:         out of range decoding Compact<u32>
   3: 
   4: Could not decode `UntrackedSymbol::id`:
   4:     out of range decoding Compact<u32>
   4: 
   5: out of range decoding Compact<u32>

The v15 metadata is stabilised in 1.0.0 release.