[1.x] Validates Swoole Tables string column types

[nunomaduro]

This pull request addresses #173, by validating Swoole Tables string column types.

// Assuming...
$table->column('string', Table::TYPE_STRING, 5);

// Before this change, the code above would set '12345' on cache instead of '123456', ignoring part of the string that exceeds the 5 bytes.
// After this change, Octane now throws an `ValueTooLargeForColumnException` exception because '123456' is indeed to large for the column.
$table->set('rows-id', ['column-name' => '123456']);