Refactor Tecan pump driver and tests for integration with Navigate device layer

[juhelh]

This PR updates the XCaliburPump implementation to make it compatible with the Navigate device layer and naming conventions.

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Changes based on integration feedback

• File naming: Renamed to tecan.py to match manufacturer name.
• Class naming: Renamed to XCaliburPump to match device model.
• Constructor updated: Now follows the standard device interface.
• Connection interface: Added required @classmethod connect(...) for serial devices.
• Error handling: Replaced RuntimeError, ValueError, etc., with UserVisibleException.

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Tests

• Test suite updated to match refactored interface.
• Uses pytest and mocks Serial with a custom FakeSerial class.

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Notes

• This PR replaces the previous one (Add Tecan XCalibur pump interface and test suite #1122), which was accidentally broken by an incorrect force-push.
• This branch contains only the intended files:
  • tecan.py
  • test_tecan.py
    with no unrelated history or experimental code.