Refactoring to remove late variables and cyclic dependencies (#247)

* Cleaned up `config_handler.dart`

* Cleaned up `log_handler.dart`

* Cleaned up `session.dart`

* Clean up `survey_handler.dart`

* Confighandler no longer late variable

* Remove `Initializer` dependency from `ConfigHandler`

* Remove `late` variable for `_clientId`

* Consolidate `Session` into `UserProperty`

* Sort members + swap error messages for tests

* `dart format .`

* Fix tests + note a TODO for `package:file`

* `..run()`

* Remove `UserProperty.initialize` method

* Remove `ErrorHandler` + no late for userprop and loghandler

* Fix test

* Make userprop variable private

* Move configHandler to constructor initializer

* Remove unnecessary parameters for log handler

* Add'l documentation

* Remove unused params for survey handler

* Changelog update + dartdocs

* Bump version to `6.0.0`

* Remove `Initializer` abstraction, sub for functions

* Fix test for session file modified timestamp

* Remove `sessionIdOverride` for session initializer

* Clean up CHANGELOG

* Fix failing test

* Format fix

pkgs/unified_analytics/CHANGELOG.md

@@ -1,3 +1,10 @@
+## 6.0.0-wip
+
+- Consolidate `Session` functionality into `UserProperty` to prevent race condition crash where session logic crashed before initializing `UserProperty`
+- Get rid of `late` variables throughout implementation class, `AnalyticsImpl`
+- Any error events (`Event.analyticsException`) encountered within package will be sent when invoking `Analytics.close`; replacing `ErrorHandler` functionality
+- Exposing new method for `FakeAnalytics.sendPendingErrorEvents` to send error events on command
+
 ## 5.8.8
 
 - [Bug fix](https://github.com/dart-lang/tools/issues/252) rewrite the other call site for the session file
@@ -8,7 +15,7 @@
 
 ## 5.8.6
 
-- Refactored session handler class to use the last modified timestamp as the last ping value
+- Refactored session handler class to use the last modified timestamp as the last ping value to prevent writing to file with each send
 - Bumping intl package to 0.19.0 to fix version solving issue with flutter_tools
 
 ## 5.8.5

pkgs/unified_analytics/example/serving_surveys.dart

@@ -5,6 +5,7 @@
 import 'package:clock/clock.dart';
 import 'package:file/file.dart';
 import 'package:file/memory.dart';
+import 'package:path/path.dart' as p;
 
 import 'package:unified_analytics/src/constants.dart';
 import 'package:unified_analytics/src/enums.dart';
@@ -57,8 +58,11 @@ void main() async {
         fs: fs,
         platform: DevicePlatform.macos,
         surveyHandler: FakeSurveyHandler.fromList(
-          homeDirectory: home,
-          fs: fs,
+          dismissedSurveyFile: fs.file(p.join(
+            home.path,
+            kDartToolDirectoryName,
+            kDismissedSurveyFileName,
+          )),
           initializedSurveys: [
             Survey(
               uniqueId: 'uniqueId',