Share SqlTokenizer with the statement INSERT detection #155

The tokenizer consolidation for SqlTableReference and LibsqlResultSetMetaData landed in #154. Two copies remain outside that scope. LibsqlStatement has its own skipQuoted, and LibsqlPreparedStatement has tokenize and skipQuoted, used by the INSERT, REPLACE, and WITH...INSERT generated-keys detection. They duplicate SqlTokenizer and can drift from it.

Expected: move both onto SqlTokenizer, keep the generated-keys semantics unchanged, and add behavior tests for INSERT, REPLACE, WITH...INSERT, comments, and quoted identifiers.