refactor: linting de widgets de layout y utilidades

Ajustes de estilo/linting en los helpers centered* de layout,
appIntroPage, roundedButton, secretLoader y utils (refactor pendiente).

lib/layout/abstractCenteredColumn.dart

@@ -2,15 +2,15 @@ import 'package:flutter/material.dart';
 
 abstract class AbstractCenteredColumn extends Column {
   AbstractCenteredColumn({
-    Key key,
-    MainAxisAlignment mainAxisAlignment,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    MainAxisAlignment? mainAxisAlignment,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,
-          mainAxisAlignment: mainAxisAlignment,
+          mainAxisAlignment: mainAxisAlignment ?? MainAxisAlignment.start,
           mainAxisSize: MainAxisSize.max,
           crossAxisAlignment: CrossAxisAlignment.center,
           textDirection: textDirection,

lib/layout/abstractCenteredRow.dart

@@ -2,15 +2,15 @@ import 'package:flutter/material.dart';
 
 abstract class AbstractCenteredRow extends Row {
   AbstractCenteredRow({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
     mainAxisAlignment,
-    List<Widget> children: const <Widget>[],
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,
-          mainAxisAlignment: mainAxisAlignment,
+          mainAxisAlignment: mainAxisAlignment ?? MainAxisAlignment.start,
           mainAxisSize: MainAxisSize.max,
           crossAxisAlignment: CrossAxisAlignment.center,
           textDirection: textDirection,

lib/layout/centeredColumn.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredColumn.dart';
 
 class CenteredColumn extends AbstractCenteredColumn {
   CenteredColumn({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,

lib/layout/centeredMaxWidget.dart

@@ -4,10 +4,10 @@ import 'centeredRow.dart';
 
 class CenteredMaxWidget extends CenteredColumn {
   CenteredMaxWidget({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
     children: <Widget>[new CenteredRow(children: children)],
           key: key,

lib/layout/centeredRow.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredRow.dart';
 
 class CenteredRow extends AbstractCenteredRow {
   CenteredRow({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,

lib/layout/centeredSpaceAroundColumn.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredColumn.dart';
 
 class CenteredSpaceAroundColumn extends AbstractCenteredColumn {
   CenteredSpaceAroundColumn({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,

lib/layout/centeredSpaceAroundRow.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredRow.dart';
 
 class CenteredSpacedAroundRow extends AbstractCenteredRow {
   CenteredSpacedAroundRow({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,

lib/layout/centeredSpaceBetweenColumn.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredColumn.dart';
 
 class CenteredSpaceBetweenColumn extends AbstractCenteredColumn {
   CenteredSpaceBetweenColumn({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,

lib/layout/centeredSpaceBetweenRow.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredRow.dart';
 
 class CenteredSpacedBetweenRow extends AbstractCenteredRow {
   CenteredSpacedBetweenRow({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,

lib/layout/centeredSpaceEvenlyColumn.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredColumn.dart';
 
 class CenteredSpaceEvenlyColumn extends AbstractCenteredColumn {
   CenteredSpaceEvenlyColumn({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,

lib/layout/centeredSpaceEvenlyRow.dart

@@ -3,10 +3,10 @@ import 'abstractCenteredRow.dart';
 
 class CenteredSpacedEvenlyRow extends AbstractCenteredRow {
   CenteredSpacedEvenlyRow({
-    Key key,
-    TextDirection textDirection,
-    TextBaseline textBaseline,
-    List<Widget> children: const <Widget>[],
+    Key? key,
+    TextDirection? textDirection,
+    TextBaseline? textBaseline,
+    List<Widget> children = const <Widget>[],
   }) : super(
           children: children,
           key: key,