plugin-avail: test config and coverage

[ai16z-demirix]

Is your feature request related to a problem? Please describe.

The plugin-avail package currently lacks proper test coverage. There are no tests to verify the functionality of the actions, error handling, or integration with the Avail network. This makes it difficult to ensure reliability and catch potential issues before they reach production.

Describe the solution you'd like

Add comprehensive test coverage using vitest for the plugin-avail package, including:

• Unit tests for all actions (submitData, transfer)
• Error handling tests
• Mock implementations for Avail SDK
• Test utilities and fixtures
• Proper test configuration
  This will help ensure code reliability and make it easier to maintain and extend the package in the future.

Describe alternatives you've considered

Additional context