This commit introduces a number of new tests for the `pkg/mining` package,
increasing the overall test coverage from 8.2% to 41.4%.
The following changes were made:
- Added tests for the `XMRigMiner` struct, including its methods for
installation, starting, stopping, and getting stats.
- Added tests for the `Service` layer, including the API endpoints for
listing, starting, stopping, and getting stats for miners.
- Added tests for the `Manager`, including starting and stopping multiple
miners, collecting stats, and getting hashrate history.
- Introduced a `ManagerInterface` to decouple the `Service` layer from the
concrete `Manager` implementation, facilitating testing with mocks.
- Fixed a failing test on Windows by creating a Windows-compatible
dummy executable.
- Improved encapsulation in tests by adding and using getter methods for
private fields.
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