reduce verbosity of "Persisted user chains" (#3395)

## Motivation

This line is printed repeatedly and is not that useful.

## Proposal

Make it `trace` level.

## Test Plan

CI

linera-client/src/config.rs

@@ -134,7 +134,7 @@ impl<W: Persist<Target = Wallet>> Persist for WalletState<W> {
         self.wallet
             .mutate(|w| w.refresh_prng_seed(&mut self.prng))
             .await?;
-        tracing::debug!("Persisted user chains");
+        tracing::trace!("Persisted user chains");
         Ok(())
     }