Improve typing in `prefect.server.events` #19309

Job	Run time
docker, python:3.9	5m 21s
docker, python:3.10	5m 16s
Server Tests - python:3.9, postgres:14	6m 21s
docker, python:3.11	4m 53s
Server Tests - python:3.10, postgres:14	6m 2s
typesafety	2m 4s
docker, python:3.12	5m 15s
Server Tests - python:3.11, postgres:14	5m 25s
Server Tests - python:3.12, postgres:14	5m 34s
Server Tests - python:3.9, sqlite	6m 31s
Server Tests - python:3.10, sqlite	6m 37s
Server Tests - python:3.11, sqlite	5m 47s
Server Tests - python:3.12, sqlite	6m 22s
Database and Orchestration Tests - python:3.9, postgres:14	7m 20s
Database and Orchestration Tests - python:3.10, postgres:14	7m 11s
Database and Orchestration Tests - python:3.11, postgres:14	6m 12s
Database and Orchestration Tests - python:3.12, postgres:14	7m 4s
Database and Orchestration Tests - python:3.9, sqlite	8m 54s
Database and Orchestration Tests - python:3.10, sqlite	8m 25s
Database and Orchestration Tests - python:3.11, sqlite	7m 43s
Database and Orchestration Tests - python:3.12, sqlite	9m 10s
Client Tests - python:3.9, postgres:14	10m 17s
Client Tests - python:3.10, postgres:14	9m 46s
Client Tests - python:3.11, postgres:14	8m 38s
Client Tests - python:3.12, postgres:14	9m 42s
Runner, Worker, Settings, Input, and CLI Tests - python:3.9, postgres:14	6m 57s
Runner, Worker, Settings, Input, and CLI Tests - python:3.10, postgres:14	6m 38s
Runner, Worker, Settings, Input, and CLI Tests - python:3.11, postgres:14	5m 52s
Runner, Worker, Settings, Input, and CLI Tests - python:3.12, postgres:14	6m 45s
	3h 18m 2s

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