pager: bump default page cache size from 10 to 1000 pages

```
Gnuplot not found, using plotters backend
Execute `SELECT count() FROM users`/limbo_execute_select_count
                        time:   [12.867 µs 12.958 µs 13.104 µs]
                        change: [-91.233% -91.178% -91.120%] (p = 0.00 < 0.05)
                        Performance has improved.
```

core/lib.rs

@@ -166,7 +166,7 @@ impl Database {
             None
         };
 
-        let shared_page_cache = Arc::new(RwLock::new(DumbLruPageCache::new(10)));
+        let shared_page_cache = Arc::new(RwLock::new(DumbLruPageCache::new(1000)));
         let schema = Arc::new(RwLock::new(Schema::new()));
         let db = Database {
             mv_store,