fix: read metadata and runtime version at the head, not the finalized block

Cargo.toml

@@ -142,6 +142,7 @@ qp-wormhole-circuit-builder = { version = "4.3.0" }
 sha2 = "0.10"
 
 [dev-dependencies]
+jsonrpsee = { version = "0.24", features = ["server"] }
 qp-poseidon-core = "3.1.0"
 serial_test = "3.1"
 tempfile = "3.8.1"

LIBRARY_USAGE.md

@@ -51,6 +51,16 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 }
 ```
 
+`QuantusClient::new` reads the runtime version and metadata from the current best block, so a
+runtime upgrade is visible as soon as it enacts. To decode an older block, ask for a client pinned
+to that block. It shares the connection and only fetches metadata when the block ran a different
+runtime:
+
+```rust
+let at_finalized = client.at_block(finalized_hash).await?;
+let events = at_finalized.client().blocks().at(finalized_hash).await?.events().await?;
+```
+
 ### 3. Loading a Wallet for Transactions
 
 ```rust