888: Fix get_duplicate_forecasts() deprecation message

[nikosbosse]

CLAUDE: Fixes the deprecation warning added in #1148 (#888), before it ships in 2.3.0.

Problem

Calling get_duplicate_forecasts() on a plain data.frame without type warned:

The `type` argument of `get_duplicate_forecasts()` is deprecated as of scoringutils 2.2.0.
ℹ Pass `type` (e.g. "quantile", "sample") to detect type-specific duplicates on plain data.frames.

That says the opposite of what is meant. The type argument isn't deprecated; calling without it is. The details line then tells users to pass type, which contradicts the first line. The version is also wrong: the change ships in 2.3.0.

Fix

The message now reads:

Calling `get_duplicate_forecasts()` on a data.frame without specifying `type`
was deprecated in scoringutils 2.3.0.
ℹ Pass `type` (e.g. "quantile", "sample") to detect type-specific duplicates on
  plain data.frames.

• The custom text uses lifecycle::deprecate_warn(what = I(...)), which needs lifecycle ≥ 1.0.2 (from 2022). DESCRIPTION now requires that version.
• The deprecation test now checks the wording and the version.

The argument order stays as #1148 has it: data, forecast_unit, type, counts. Earlier revisions of this PR moved type and added a check on its value; after discussion we dropped that in favour of this minimal fix.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.18%. Comparing base (aa3d834) to head (f1c5819).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1232   +/-   ##
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  Coverage   99.18%   99.18%           
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  Files          41       41           
  Lines        2331     2333    +2     
=======================================
+ Hits         2312     2314    +2     
  Misses         19       19           

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[nikosbosse]

lgtm.

I slightly prefer the order of types, counts vs. counts, types, but not breaking code is also nice