fix: LocalDate toString error

[amondnet]

Error Logs

type '(LocalDate, StringBuffer) => void' is not a subtype of type 'Object' of 'value'
               type '(LocalDate, StringBuffer) => void' is not a subtype of type 'Object' of 'value'
               #0      List.add (dart:core-patch/growable_array.dart)
               #1      SteppedPatternBuilder.addFormatAction (package:time_machine/src/text/patterns/stepped_pattern_builder.dart:142:88)
               #2      DatePatternHelper.createDayHandler.<anonymous closure> (package:time_machine/src/text/patterns/date_pattern_helper.dart:127:19)
               #3      SteppedPatternBuilder.parseCustomPattern (package:time_machine/src/text/patterns/stepped_pattern_builder.dart:72:16)
               #4      LocalDatePatternParser.parsePattern (package:time_machine/src/text/localdate_pattern_parser.dart:62:20)
               #5      new FixedFormatInfoPatternParser.<anonymous closure> (package:time_machine/src/text/fixed_format_info_pattern_parser.dart:21:88)
               #6      Cache.getOrAdd (package:time_machine/src/utility/cache.dart:55:32)
               #7      FixedFormatInfoPatternParser.parsePattern (package:time_machine/src/text/fixed_format_info_pattern_parser.dart:26:54)
               #8      LocalDatePatterns.format (package:time_machine/src/text/localdate_pattern.dart:26:12)
               #9      LocalDate.toString (package:time_machine/src/localdate.dart:591:25)

[SteveAlexander]

Thanks for posting a fix here. Couple of things we should consider:

1. This is caused by a bug in Dart that manifests only on Android. The bug is here, and is now closed: type '(String, StringBuffer) => Null' is not a subtype of type 'Object' of 'value' dart-lang/sdk#46165

So, the fix will be available in a Dart version pretty soon. If we make this change to time_machine, I expect we'll want to revert it once the Dart fix hits the stable channel.

2. I think it would be better to use Object? than dynamic as a temporary workaround, as it's more explicit about what the type is.

Interested in hearing your thoughts on these!

Thanks again for offering this PR.