Adding time zone handling

[MrCsabaToth]

UA and Training Peaks requires time zone designation

[MrCsabaToth]

For now I won't use .toUtc(), .toLocal(), or fromMillisecondsSinceEpoch(..., isUtc: true). Here are some DaartPad experiments:

  final now = DateTime.now();
  debugPrint("now $now");
  final epoch = now.millisecondsSinceEpoch;
  debugPrint("epoch $epoch");
  final dt = DateTime.fromMillisecondsSinceEpoch(epoch);
  debugPrint("dt $dt");
  final utcDt = DateTime.fromMillisecondsSinceEpoch(epoch, isUtc: true);
  debugPrint("utcDt $utcDt");

  final utcNow = now.toUtc();
  debugPrint("UTC Now $utcNow");
  final utcEpoch = utcNow.millisecondsSinceEpoch;
  debugPrint("UTC epoch $utcEpoch");
  final dtUtc = DateTime.fromMillisecondsSinceEpoch(utcEpoch);
  debugPrint("dt UTC $dtUtc");
  final utcDtUtc = DateTime.fromMillisecondsSinceEpoch(utcEpoch, isUtc: true);
  debugPrint("UTC dt UTC $utcDtUtc");

now 2021-08-28 09:29:22.693
epoch 1630168162693
dt 2021-08-28 09:29:22.693
utcDt 2021-08-28 16:29:22.693Z
UTC Now 2021-08-28 16:29:22.693Z
UTC epoch 1630168162693
dt UTC 2021-08-28 09:29:22.693
UTC dt UTC 2021-08-28 16:29:22.693Z

[MrCsabaToth]

Took a look at https://pub.dev/packages/timezone but I decided to go with https://pub.dev/packages/flutter_native_timezone because it has a simple API which makes more sense.

[MrCsabaToth]

https://pub.dev/packages/flutter_native_timezone shows empty string in debug. I may need to involve https://pub.dev/packages/timezone as well as a fallback?

[MrCsabaToth]

It turns out that it was just a UI problem, the string is not empty it just needed it setState because it's async.

[MrCsabaToth]

Now I need to address #139: per time zone based tracks