chore: mockito dependency updates, dependency changes & analysis warnings/errors

[russellwheatley]

Description

This PR affects auth, core, messaging database & firestore packages.

• mockito dependency breaks the all_plugins/tests check for github actions. It made a breaking change to the API which this PR resolves.
• removed UUID dependency in auth_example.
• changed js dependency version to be less restrictive in storage_web: js: ^0.6.3-nullsafety.3 (i.e. uses caret syntax).
• removed deprecated BinaryMessages API and replaced with ServicesBinding.instance.defaultBinaryMessenger as recommended here.
• commented out runTransaction test as it was failing. Needs further investigation. Test fixed.

Related Issues

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Checklist

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• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
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Breaking Change

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• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.