prepared: enable cached result metadata optimization by default

We already cache the metadata on cpp-rust-driver side (see CassPrepared::result_metadata field),
thus we can enable the optimization on rust-driver side as well. This will prevent the server
from sending redundant bytes representing a result metadata during EXECUTE.

NOTE: We are aware that it makes cached metadata immutable. It is expected, though - there
is an integration test for this for CQL protocol v4 (AlterDoesntUpdateColumnCount).
This issue is addressed in CQL protocol v5, but Scylla doesn't support it yet, and probably
won't support it in the near future.

Author: muzarski

scylla-rust-wrapper/src/prepared.rs

@@ -23,7 +23,17 @@ pub struct CassPrepared {
 }
 
 impl CassPrepared {
-    pub fn new_from_prepared_statement(statement: PreparedStatement) -> Self {
+    pub fn new_from_prepared_statement(mut statement: PreparedStatement) -> Self {
+        // We already cache the metadata on cpp-rust-driver side (see CassPrepared::result_metadata field),
+        // thus we can enable the optimization on rust-driver side as well. This will prevent the server
+        // from sending redundant bytes representing a result metadata during EXECUTE.
+        //
+        // NOTE: We are aware that it makes cached metadata immutable. It is expected, though - there
+        // is an integration test for this for CQL protocol v4 (AlterDoesntUpdateColumnCount).
+        // This issue is addressed in CQL protocol v5, but Scylla doesn't support it yet, and probably
+        // won't support it in the near future.
+        statement.set_use_cached_result_metadata(true);
+
         let variable_col_data_types = statement
             .get_variable_col_specs()
             .iter()