refactor: FaultyExtractor async-hop + double style consistency

[Chris-Wolfgang]

Pure source cleanup from code review — no public-API change (zero PublicAPI.txt edits required).

Changes

1. FaultyExtractor.ExtractWorkerAsync async-hop placement. Moved await Task.Yield() from after the loop/finally (where it sat below the ThrowAfterCompletion throw and was therefore unreachable on the ThrowAfterCompletion and MaximumItemCount yield break paths) to the top of the method, right after the initial token.ThrowIfCancellationRequested() — mirroring TestExtractor.ExtractWorkerAsync. The comment now accurately states it runs on every exit path. The old misleading trailing comment is removed.
2. Style consistency (no behaviour change):
   • Worker-method signatures use the CLAUDE.md Allman-paren form (( and ) on their own lines) in TestLoader, FaultyLoader, TestTransformer, FaultyTransformer — matching the extractors.
   • CreateProgressReport() uses target-typed new(CurrentItemCount) across all doubles (was new Report(...) in the four loaders/transformers).
   • TestLoader.GetCollectedItems() snapshot switched from _buffer.ToList() to _buffer.ToArray() so both loaders use the same cheaper fixed-length snapshot; return type unchanged (IReadOnlyList<T>?).
   • Reworded the TestTransformer/FaultyTransformer parameterless-ctor <summary> from "default production timer" (inaccurate — the ctor sets no timer) to "default base-class progress timer".

Verification

• dotnet build ETL-Test-Kit.slnx -c Release → 0 warnings / 0 errors, all TFMs (net462; netstandard2.0; net481; net8.0; net10.0).
• Tests -c Release -f net8.0 → all green (355 = 233 Xunit contract + 122 unit).

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