fix(instrument): silence get_idn warning on virtual instruments

[officialasishkumar]

Summary

Closes #4611.

Instrument.get_idn calls self.ask("*IDN?") which delegates to ask_raw. The base Instrument class leaves ask_raw as a stub that raises NotImplementedError, so any virtual instrument that does not override it — e.g. a purely in-memory model — always produced a warning on every call to get_idn. That regularly appears when a virtual instrument is added to a Station and the station queries its IDN during snapshotting.

This PR narrows the except block so that NotImplementedError is treated as the expected signal of a virtual instrument and returns the default None-valued dict silently. All other exceptions still go through self.log.warning with exc_info=True, so genuine communication failures remain visible.

• src/qcodes/instrument/instrument.py: split the broad except Exception so NotImplementedError is handled without a warning.
• tests/test_instrument.py: two regression tests — one confirms no warning is emitted for a virtual instrument without ask_raw, the other confirms that unexpected errors (e.g. RuntimeError from a broken ask_raw) still produce a warning.
• Added a newsfragment.

Test plan

• pytest tests/test_instrument.py — 34 passed locally, including the two new tests.
• pytest tests/test_instrument.py -k get_idn — 3 passed.

[Copilot]

Pull request overview

This PR updates Instrument.get_idn to treat NotImplementedError (raised by the base Instrument.ask_raw stub) as an expected condition for virtual/in-memory instruments, avoiding spurious warnings while keeping warnings for genuine unexpected failures.

Changes:

• Handle NotImplementedError in Instrument.get_idn without logging a warning and return the default None-valued IDN dict.
• Add regression tests ensuring virtual instruments don’t warn, while other exceptions still do.
• Add a Towncrier newsfragment documenting the behavioral change.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/qcodes/instrument/instrument.py	Narrows exception handling in get_idn to silence warnings only for NotImplementedError.
tests/test_instrument.py	Adds regression coverage for the new get_idn warning behavior.
docs/changes/newsfragments/4611.improved	Documents the change in user-visible behavior for virtual instruments.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.63%. Comparing base (36967bf) to head (ddaa400).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8038   +/-   ##
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  Coverage   70.63%   70.63%           
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  Files         333      333           
  Lines       32330    32332    +2     
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+ Hits        22837    22839    +2     
  Misses       9493     9493           

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