feat: WIP fee slider widget

lib/widgets/fee_slider.dart

@@ -0,0 +1,56 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+import 'package:stackwallet/utilities/text_styles.dart';
+
+class FeeSlider extends StatefulWidget {
+  const FeeSlider({
+    super.key,
+    required this.onSatVByteChanged,
+  });
+
+  final void Function(int) onSatVByteChanged;
+
+  @override
+  State<FeeSlider> createState() => _FeeSliderState();
+}
+
+class _FeeSliderState extends State<FeeSlider> {
+  static const int min = 1;
+  static const int max = 10;
+
+  double sliderValue = 0;
+
+  int rate = min;
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      children: [
+        Row(
+          mainAxisAlignment: MainAxisAlignment.spaceBetween,
+          children: [
+            Text(
+              "sat/vByte",
+              style: STextStyles.smallMed12(context),
+            ),
+            Text(
+              "$rate",
+              style: STextStyles.smallMed12(context),
+            ),
+          ],
+        ),
+        Slider(
+          value: sliderValue,
+          onChanged: (value) {
+            setState(() {
+              sliderValue = value;
+              rate = pow(sliderValue * (max - min) + min, 4).toInt();
+            });
+            widget.onSatVByteChanged(rate);
+          },
+        ),
+      ],
+    );
+  }
+}