docs: fix non-compiling Rust session-limits example (#2082)

The Rust tab of docs/features/session-limits.md called SessionConfig::new(),
which does not exist -- SessionConfig is constructed via Default plus builder
methods, so copying the example produced error[E0599]. Use
SessionConfig::default() so the documented snippet compiles against the SDK it
ships with. The neighboring resume example already uses the real
ResumeSessionConfig::new(session_id) and is unchanged.

Co-authored-by: examon <examon@users.noreply.github.com>

Author: examon

docs/features/session-limits.md

@@ -131,7 +131,7 @@ let limits = SessionLimitsConfig {
 
 let session = client
     .create_session(
-        SessionConfig::new()
+        SessionConfig::default()
             .approve_all_permissions()
             .with_session_limits(limits.clone()),
     )