Adds an `on_timer` event to agents. #236

Job	Run time
Build Example Application UIs (stocks_simulated/ui, npm install && npm run build)	15s
Code Coverage	19m 43s
Check (windows-latest)	10m 10s
Clippy	7m 0s
Check (ubuntu-latest)	6m 1s
Documentation	6m 47s
Check (macos-latest)	4m 9s
Rustfmt	20s
Test (windows-latest)	15m 7s
Test (ubuntu-latest)	8m 9s
Test (macos-latest)	6m 12s
	1h 23m 53s

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