feat: add ds_mysql.hpp convenience umbrella header

Adds lib/include/ds_mysql.hpp that includes the three top-level headers
needed to work with the library:
  - mysql_database.hpp  (connection, queries, result sets)
  - mysql_metadata.hpp  (runtime schema introspection)
  - sql_extension.hpp   (extra query-builder helpers)

All other headers (sql.hpp, schema_generator.hpp, column_field.hpp,
varchar_field.hpp, sql_identifiers.hpp, sql_temporal.hpp, mysql_config.hpp,
credentials.hpp, …) are pulled in transitively.

Update both examples to use #include "ds_mysql.hpp" instead of the
individual per-header includes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Pierre-Luc Gagné

examples/basic_query.cpp

@@ -25,12 +25,7 @@
 #include <print>
 #include <string>
 
-#include "ds_mysql/column_field.hpp"
-#include "ds_mysql/mysql_config.hpp"
-#include "ds_mysql/mysql_database.hpp"
-#include "ds_mysql/sql.hpp"
-#include "ds_mysql/sql_temporal.hpp"
-#include "ds_mysql/varchar_field.hpp"
+#include "ds_mysql.hpp"
 
 // ===================================================================
 // Define a typed table struct.

examples/schema_generation.cpp

@@ -14,13 +14,7 @@
 #include <print>
 #include <string>
 
-#include "ds_mysql/column_field.hpp"
-#include "ds_mysql/mysql_database.hpp"
-#include "ds_mysql/schema_generator.hpp"
-#include "ds_mysql/sql.hpp"
-#include "ds_mysql/sql_identifiers.hpp"
-#include "ds_mysql/sql_temporal.hpp"
-#include "ds_mysql/varchar_field.hpp"
+#include "ds_mysql.hpp"
 
 // ===================================================================
 // Define a 'user' table

lib/include/ds_mysql.hpp

@@ -0,0 +1,17 @@
+#pragma once
+
+// Convenience header — include everything needed to work with DSMySQL.
+//
+// Transitively provides:
+//   mysql_database.hpp  — database connection, query execution, result sets
+//   sql.hpp             — query builder (SELECT / INSERT / UPDATE / DELETE / ...)
+//   sql_extension.hpp   — additional query-builder helpers (ROUND, FORMAT, ...)
+//   mysql_metadata.hpp  — runtime metadata helpers (column info, schema introspection)
+//
+// All other library headers (column_field, schema_generator, sql_identifiers,
+// sql_temporal, varchar_field, text_field, mysql_config, credentials, …) are
+// pulled in transitively by the four headers above.
+
+#include "ds_mysql/mysql_database.hpp"
+#include "ds_mysql/mysql_metadata.hpp"
+#include "ds_mysql/sql_extension.hpp"