lint: optimize enum types and fix reserved identifiers in Base/PgSQL hostgroups

performance-enum-size fixes:
- p_mysql_error_type: add uint8_t underlying type (2 values)
- p_pgsql_error_type: add uint8_t underlying type (2 values)
- p_hg_dyn_gauge: add uint8_t underlying type (5 values)
- p_hg_dyn_counter: add uint8_t underlying type (9 values)
- PgSQL_p_hg_dyn_gauge: add uint8_t underlying type (5 values)
- PgSQL_p_hg_dyn_counter: add uint8_t underlying type (9 values)

bugprone-reserved-identifier fixes:
- Rename __size -> SIZE_ in all metric enums to avoid reserved identifier
- Update std::array size references to use new SIZE_ enum values

Applies same fixes as MySQL_HostGroups_Manager.h to:
- Base_HostGroups_Manager.h (base class)
- PgSQL_HostGroups_Manager.h (PostgreSQL implementation)

include/Base_HostGroups_Manager.h

@@ -482,7 +482,7 @@ struct p_hg_counter {
 		myhgm_myconnpool_reset,
 		myhgm_myconnpool_destroy,
 		auto_increment_delay_multiplex,
-		__size
+		SIZE_
 	};
 };
 
@@ -490,12 +490,12 @@ struct p_hg_gauge {
 	enum metric {
 		server_connections_connected = 0,
 		client_connections_connected,
-		__size
+		SIZE_
 	};
 };
 
 struct p_hg_dyn_counter {
-	enum metric {
+	enum metric : uint8_t {
 		conn_pool_bytes_data_recv = 0,
 		conn_pool_bytes_data_sent,
 		connection_pool_conn_err,
@@ -504,22 +504,22 @@ struct p_hg_dyn_counter {
 		gtid_executed,
 		proxysql_mysql_error,
 		mysql_error,
-		__size
+		SIZE_
 	};
 };
 
-enum class p_mysql_error_type {
+enum class p_mysql_error_type : uint8_t {
 	mysql,
 	proxysql
 };
 
 struct p_hg_dyn_gauge {
-	enum metric {
+	enum metric : uint8_t {
 		connection_pool_conn_free = 0,
 		connection_pool_conn_used,
 		connection_pool_latency_us,
 		connection_pool_status,
-		__size
+		SIZE_
 	};
 };
 
@@ -915,12 +915,12 @@ class MySQL_HostGroups_Manager {
 		//////////////////////////////////////////////////////
 
 		/// Prometheus metrics arrays
-		std::array<prometheus::Counter*, p_hg_counter::__size> p_counter_array {};
-		std::array<prometheus::Gauge*, p_hg_gauge::__size> p_gauge_array {};
+		std::array<prometheus::Counter*, p_hg_counter::SIZE_> p_counter_array {};
+		std::array<prometheus::Gauge*, p_hg_gauge::SIZE_> p_gauge_array {};
 
 		// Prometheus dyn_metrics families arrays
-		std::array<prometheus::Family<prometheus::Counter>*, p_hg_dyn_counter::__size> p_dyn_counter_array {};
-		std::array<prometheus::Family<prometheus::Gauge>*, p_hg_dyn_gauge::__size> p_dyn_gauge_array {};
+		std::array<prometheus::Family<prometheus::Counter>*, p_hg_dyn_counter::SIZE_> p_dyn_counter_array {};
+		std::array<prometheus::Family<prometheus::Gauge>*, p_hg_dyn_gauge::SIZE_> p_dyn_gauge_array {};
 
 		/// Prometheus connection_pool metrics
 		std::map<std::string, prometheus::Counter*> p_conn_pool_bytes_data_recv_map {};

include/PgSQL_HostGroups_Manager.h

@@ -287,7 +287,7 @@ struct PgSQL_p_hg_counter {
 		pghgm_pgconnpool_reset,
 		pghgm_pgconnpool_destroy,
 		auto_increment_delay_multiplex,
-		__size
+		SIZE_
 	};
 };
 
@@ -295,12 +295,12 @@ struct PgSQL_p_hg_gauge {
 	enum metric {
 		server_connections_connected = 0,
 		client_connections_connected,
-		__size
+		SIZE_
 	};
 };
 
 struct PgSQL_p_hg_dyn_counter {
-	enum metric {
+	enum metric : uint8_t {
 		conn_pool_bytes_data_recv = 0,
 		conn_pool_bytes_data_sent,
 		connection_pool_conn_err,
@@ -309,22 +309,22 @@ struct PgSQL_p_hg_dyn_counter {
 		gtid_executed,
 		proxysql_pgsql_error,
 		pgsql_error,
-		__size
+		SIZE_
 	};
 };
 
-enum class p_pgsql_error_type {
+enum class p_pgsql_error_type : uint8_t {
 	pgsql,
 	proxysql
 };
 
 struct PgSQL_p_hg_dyn_gauge {
-	enum metric {
+	enum metric : uint8_t {
 		connection_pool_conn_free = 0,
 		connection_pool_conn_used,
 		connection_pool_latency_us,
 		connection_pool_status,
-		__size
+		SIZE_
 	};
 };
 
@@ -639,12 +639,12 @@ class PgSQL_HostGroups_Manager : public Base_HostGroups_Manager<PgSQL_HGC> {
 		//////////////////////////////////////////////////////
 
 		/// Prometheus metrics arrays
-		std::array<prometheus::Counter*, PgSQL_p_hg_counter::__size> p_counter_array {};
-		std::array<prometheus::Gauge*, PgSQL_p_hg_gauge::__size> p_gauge_array {};
+		std::array<prometheus::Counter*, PgSQL_p_hg_counter::SIZE_> p_counter_array {};
+		std::array<prometheus::Gauge*, PgSQL_p_hg_gauge::SIZE_> p_gauge_array {};
 
 		// Prometheus dyn_metrics families arrays
-		std::array<prometheus::Family<prometheus::Counter>*, PgSQL_p_hg_dyn_counter::__size> p_dyn_counter_array {};
-		std::array<prometheus::Family<prometheus::Gauge>*, PgSQL_p_hg_dyn_gauge::__size> p_dyn_gauge_array {};
+		std::array<prometheus::Family<prometheus::Counter>*, PgSQL_p_hg_dyn_counter::SIZE_> p_dyn_counter_array {};
+		std::array<prometheus::Family<prometheus::Gauge>*, PgSQL_p_hg_dyn_gauge::SIZE_> p_dyn_gauge_array {};
 
 		/// Prometheus connection_pool metrics
 		std::map<std::string, prometheus::Counter*> p_conn_pool_bytes_data_recv_map {};