Fix serveral issues with the DCD module

[robin-checkmk]

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• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
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• Documentation content changes
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What is the current behavior?

Describe the current behavior that you are modifying, or link to a relevant issue.

Four concrete issues:

1. Bug — logger.set_loglevel(2) (line 590): immediately overrides logger.set_loglevel(module._verbosity) on line 589, so verbosity is always hardcoded to 2 regardless of -v flags. Leftover
   debug line.
2. DCDHTTPCodes class: an unnecessary class wrapping plain dicts. dcd_metricbackend.py uses module-level HTTP_CODES_* dicts directly — cleaner and consistent with the rest of the
   collection.
3. Multi-line docstrings on every method: violates the no-comments convention we follow. They describe what the code does, not why, and are redundant given well-named identifiers. All of
   it should be removed.
4. except Exception as e in run_module: catches everything including programming errors, masking real bugs. dcd_metricbackend.py has no such catch. Should be removed.

Minor/secondary: json.JSONDecodeError (line 404) should be (ValueError, TypeError) for consistency; and the stale # Is this necessary? comment on line 576 should be resolved (the answer is
no — base_argument_spec() already handles this, and the required_if there just duplicates what Ansible enforces via api_auth_type).

The bug 1 is the only one with runtime impact.

What is the new behavior?

Describe the behavior or changes that are being added by this PR.

The above issues have been fixed.

Other information

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[github-actions]

This pull request has been stale for 60 days. It will close in 7 days.