Using VB instance instead of singleton

[ygit]

Description

• Using VB instance instead of singleton

Pre-launch Checklist

• [x] The Documentation is updated accordingly, or this PR doesn't require it.
• [x] The ExampleAppChangelog is updated with related tickets, or this PR doesn't require it.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] I listed at least one issue that this PR fixes in the description above.
• [x] I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• [x] I added new tests to check the change I am making, or this PR is test-exempt.
• [x] All existing and new tests are passing.