Wrong naming of hive constant global variable

I've looked through https://dart.dev/effective-dart/design and I personally never met variable naming started from the capital letter even for constant variables in Flutter projects.

I believe that the `final HiveInterface Hive = HiveImpl();` in `hive.dart`
should be named `hive`, or any other name started from non capital letter

Start in hive.dart and inspect the declaration of the global Hive constant. Search the repository for references to its current name, update the naming consistently, and verify that the project still builds and its existing tests pass.

Written by the indexing model from the issue text.