Rename the virtual tick() override in PelicanTimer to doExpired()
and give the base Timer class a non-virtual tick() that checks for
expiration and dispatches to doExpired(). The exercise starting
point now matches SolutionEx22.
Co-authored-by: Qwen 3.8 27B <qwen3.8_27b-q3_k_xl@lmstudio.local>
porterskyandQwen 3.8 27B
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