fix: fix timer in Update timer.rs

[HarleyQeen]

The Timer component was using a last_tick field to compute elapsed time, which was only initialized in new() and never updated during normal execution. This caused the timer to always display the same duration instead of the actual time since the action began.

Fix:

Removed the unused last_tick field.

Replaced last_tick.elapsed() with start.elapsed() to correctly reflect time since the action started.

Simplified the logic in finalize() by removing unnecessary state reset.

Why:
start.elapsed() is sufficient for showing total elapsed time, and avoids redundant state tracking. This change makes the timer behave as expected and keeps the code cleaner.

[github-actions]

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[sjudson]

Duplicate of #425