sketch: refactor lowlevel server to handler pattern #434

Job	Run time
checks / pre-commit	30s
checks / readme-snippets	14s
checks / test (3.11, locked, windows-latest)	6m 49s
checks / test (3.10, lowest-direct, windows-latest)	7m 25s
checks / test (3.10, lowest-direct, ubuntu-latest)	5m 55s
checks / test (3.12, locked, ubuntu-latest)	6m 1s
checks / test (3.13, lowest-direct, ubuntu-latest)	5m 55s
checks / test (3.12, lowest-direct, ubuntu-latest)	6m 17s
checks / test (3.10, locked, windows-latest)	6m 22s
checks / test (3.11, locked, ubuntu-latest)	6m 7s
checks / test (3.14, lowest-direct, ubuntu-latest)	7m 25s
checks / test (3.10, locked, ubuntu-latest)	7m 22s
checks / test (3.12, lowest-direct, windows-latest)	6m 36s
checks / test (3.12, locked, windows-latest)	6m 31s
checks / test (3.13, locked, windows-latest)	6m 20s
checks / test (3.13, lowest-direct, windows-latest)	6m 24s
checks / test (3.14, lowest-direct, windows-latest)	6m 45s
checks / test (3.13, locked, ubuntu-latest)	7m 23s
checks / test (3.14, locked, windows-latest)	7m 15s
checks / test (3.14, locked, ubuntu-latest)	8m 36s
checks / test (3.11, lowest-direct, ubuntu-latest)	7m 26s
checks / test (3.11, lowest-direct, windows-latest)	6m 28s
all-green	4s
	2h 16m 10s

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