feat: add Connection::shrink_buffers, PoolConnection::close

closes #2372

sqlx-postgres/src/any.rs

@@ -57,6 +57,10 @@ impl AnyConnectionBackend for PgConnection {
         PgTransactionManager::start_rollback(self)
     }
 
+    fn shrink_buffers(&mut self) {
+        Connection::shrink_buffers(self);
+    }
+
     fn flush(&mut self) -> BoxFuture<'_, sqlx_core::Result<()>> {
         Connection::flush(self)
     }

sqlx-postgres/src/connection/mod.rs

@@ -199,6 +199,10 @@ impl Connection for PgConnection {
         })
     }
 
+    fn shrink_buffers(&mut self) {
+        self.stream.shrink_buffers();
+    }
+
     #[doc(hidden)]
     fn flush(&mut self) -> BoxFuture<'_, Result<(), Error>> {
         self.wait_until_ready().boxed()