Exporter error propagation

[asher-pem-arm]

Forward acquire/release failure reasons through the coordinator to the client.
This makes coordinator and exporter failures visible to users instead of returning only a generic lock/acquire failure.
The MR is split into focused commits:

report coordinator-side acquire/release failures to the client
preserve exporter failure reasons
report exporter command timeouts
reduce exported resource details in user-facing errors

Without this, it is hard to tell whether a failure happened in the client, coordinator, exporter.

[Emantor]

The second commit message will need an actual message instead of the title line and it may be beneficial to squash some commits.

I would like some test infrastructure for these new changes, but this requires rework of the coordinator/exporter/client testing in the testsuite first, which is out of scope for this PR.

Implementation wise this looks good and should improve our error reporting to the user.

[asher-pem-arm]

@Emantor happy to squash down to one commit if you think fits better?

[Emantor]

Yes, squashing to one commit should be fine.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 49 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.8%. Comparing base (915b591) to head (2053716).
⚠️ Report is 12 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
labgrid/remote/coordinator.py	0.0%	45 Missing ⚠️
labgrid/remote/exporter.py	0.0%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1886     +/-   ##
========================================
- Coverage    46.0%   45.8%   -0.2%     
========================================
  Files         180     180             
  Lines       14464   14498     +34     
========================================
  Hits         6654    6654             
- Misses       7810    7844     +34     

Flag	Coverage Δ
3.10	45.8% <0.0%> (-0.2%)	⬇️
3.11	45.8% <0.0%> (-0.2%)	⬇️
3.12	45.8% <0.0%> (-0.2%)	⬇️
3.13	45.8% <0.0%> (-0.2%)	⬇️
3.14	45.8% <0.0%> (-0.2%)	⬇️

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