Feature request: better error matching support

[sander2]

It would be really nice if we could pattern match on returned dispatch errors. E.g. something like

match error {
    SubxtRuntimeError::Module(MyModule::MyError) => {...}
    _ => ...,
}

Currently we have to manually check the PalletError.pallet and PalletError.error strings, and these string constants are not exposed in the generated code.

[jsdw]

I'll close this since a fix for this is proposed in #734 now :)

One won't be able to immediately pattern match, since the errors are generated via static codegen (which is optional), but an .as_root_error<runtime::Error>() will be provided to attempt to decode some ModuleError into a "pretty" static type.