rpc-v2/transaction: Generate `Invalid` events and add tests (#3784)
This PR ensures that the transaction API generates an `Invalid` events for transaction bytes that fail to decode. The spec mentioned the `Invalid` event at the jsonrpc error section, however this spec PR makes things clearer: - https://github.com/paritytech/json-rpc-interface-spec/pull/146 While at it have discovered an inconsistency with the generated events. The drop event from the transaction pool was incorrectly mapped to the `invalid` event. Added tests for the API stabilize the API soon: - https://github.com/paritytech/json-rpc-interface-spec/pull/144 Closes: https://github.com/paritytech/polkadot-sdk/issues/3083 cc @paritytech/subxt-team --------- Signed-off-by: Alexandru Vasile <[email protected]>