Add LightClient::builder() (#1088)

* Add LightClient::build()

* newline

* fmt

* Tweaks to make LightClient more like OnlineClient in interface

subxt/examples/unstable_light_client_tx_basic.rs

@@ -1,9 +1,5 @@
-use sp_keyring::AccountKeyring;
-use subxt::{
-    client::{LightClient, LightClientBuilder, OfflineClientT},
-    tx::PairSigner,
-    PolkadotConfig,
-};
+use subxt::{client::LightClient, PolkadotConfig};
+use subxt_signer::sr25519::dev;
 
 // Generate an interface that we can use from the node's metadata.
 #[subxt::subxt(runtime_metadata_path = "../artifacts/polkadot_metadata_small.scale")]
@@ -11,6 +7,7 @@ pub mod polkadot {}
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // The smoldot logs are informative:
     tracing_subscriber::fmt::init();
 
     // Create a light client by fetching the chain spec of a local running node.
@@ -20,7 +17,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     // The `12D3KooWEyoppNCUx8Yx66oV9fJnriXwCcXwDDUA2kj6vnc6iDEp` is the P2P address
     // from a local polkadot node starting with
     // `--node-key 0000000000000000000000000000000000000000000000000000000000000001`
-    let api: LightClient<PolkadotConfig> = LightClientBuilder::new()
+    let api = LightClient::<PolkadotConfig>::builder()
         .bootnodes([
             "/ip4/127.0.0.1/tcp/30333/p2p/12D3KooWEyoppNCUx8Yx66oV9fJnriXwCcXwDDUA2kj6vnc6iDEp",
         ])
@@ -28,12 +25,12 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .await?;
 
     // Build a balance transfer extrinsic.
-    let dest = AccountKeyring::Bob.to_account_id().into();
+    let dest = dev::bob().public_key().into();
     let balance_transfer_tx = polkadot::tx().balances().transfer(dest, 10_000);
 
     // Submit the balance transfer extrinsic from Alice, and wait for it to be successful
     // and in a finalized block. We get back the extrinsic events if all is well.
-    let from = PairSigner::new(AccountKeyring::Alice.pair());
+    let from = dev::alice();
     let events = api
         .tx()
         .sign_and_submit_then_watch_default(&balance_transfer_tx, &from)