Rust: fix LoadCargoConfig defaults (proc_macro_processes must be >= 1)

Setting proc_macro_processes to 0 causes an index-out-of-bounds panic
in ProcMacroServerPool::new when the proc macro server is enabled.
Use the same defaults as rust-analyzer itself (1 each).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

rust/extractor/src/config.rs

@@ -197,8 +197,8 @@ impl Config {
                 load_out_dirs_from_check: true,
                 with_proc_macro_server: self.proc_macro_server_choice(dir),
                 prefill_caches: false,
-                num_worker_threads: 0,
-                proc_macro_processes: 0,
+                num_worker_threads: 1,
+                proc_macro_processes: 1,
             },
         )
     }