feat(mysql)!: promote to v1.0.0 — BeginTx with isolation levels, Stats, bump all deps to v1.0.0

Add BeginTx(ctx, *sql.TxOptions) to Client interface for explicit transaction isolation
level control; Begin refactored as a convenience wrapper calling BeginTx(ctx, nil).
Add Stats() sql.DBStats to Component interface for connection pool observability.
Bump all micro-lib dependencies (logz, health, launcher, xerrors) from v0.9.0 to v1.0.0.
API committed as stable.

mysql_test.go

@@ -99,9 +99,10 @@ func (m *mockTx) Rollback() error
 
 type mockClient struct{ tx *mockTx }
 
-func (m *mockClient) Begin(ctx context.Context) (Tx, error)        { return m.tx, nil }
-func (m *mockClient) Ping(ctx context.Context) error               { return nil }
-func (m *mockClient) HandleError(err error) error                  { return HandleError(err) }
+func (m *mockClient) Begin(ctx context.Context) (Tx, error)                          { return m.tx, nil }
+func (m *mockClient) BeginTx(ctx context.Context, opts *sql.TxOptions) (Tx, error)   { return m.tx, nil }
+func (m *mockClient) Ping(ctx context.Context) error                                 { return nil }
+func (m *mockClient) HandleError(err error) error                                    { return HandleError(err) }
 func (m *mockClient) GetExecutor(ctx context.Context) Executor {
 	if tx, ok := ctx.Value(ctxTxKey{}).(Executor); ok {
 		return tx
@@ -143,6 +144,24 @@ func TestUnitOfWork_InjectsExecutor(t *testing.T) {
 	}
 }
 
+// --- BeginTx / Stats ---
+
+func TestComponent_BeginTx_NilDB(t *testing.T) {
+	c := &mysqlComponent{logger: newLogger()}
+	_, err := c.BeginTx(context.Background(), nil)
+	if err == nil {
+		t.Error("expected error for nil db")
+	}
+}
+
+func TestComponent_Stats_NilDB(t *testing.T) {
+	c := &mysqlComponent{logger: newLogger()}
+	stats := c.Stats()
+	if stats.MaxOpenConnections != 0 || stats.OpenConnections != 0 {
+		t.Errorf("expected zero DBStats, got %+v", stats)
+	}
+}
+
 // --- helpers ---
 
 func assertCode(t *testing.T, err error, want xerrors.Code) {