feat: Implement the == and hashCode methods for AtKey, AtValue and Metadata classes

[gkc]

- What I did

• Implemented the == and hashCode methods for AtKey, AtValue and Metadata classes

- Why I did it

• Needed a way to assert that a List contains another AtKey. Simplest possible way of achieving that is to override the default == and hashCode methods for the AtKey and Metadata classes. As I was doing it for those two classes, I decided to do it for AtValue also.

- How I did it

• Added the IDE-generated implementations without modifiations

- How to verify it

• Tests pass in this repo, and in the at_client_sdk, at_server and at_libraries repos
• Will add links to PRs once they have had a successful GitHub actions run
  • at_client_sdk: fix: Improved performance of getKeys when sharedBy is specified at_client_sdk#758
  • at_server: test: Testing with new version of at_commons before it is merged and published at_server#980
• Initially those PRs will use a dependency override to point to this branch.
• Once this branch has been reviewed, merged to trunk and the new package published, I will modify the PRs in the other repos to remove their dependency override take up the new package version

- Description for the changelog

• feat: Implement the == and hashCode methods for AtKey, AtValue and Metadata classes

[gkc]

Test runs have succeeded in at_client_sdk and at_server when using this branch. Merging.