sketch: refactor lowlevel server to handler pattern #400

Job	Run time
checks / pre-commit	38s
checks / readme-snippets	21s
checks / test (3.10, locked, ubuntu-latest)	33s
checks / test (3.10, locked, windows-latest)	1m 32s
checks / test (3.10, lowest-direct, windows-latest)	1m 14s
checks / test (3.11, lowest-direct, windows-latest)	1m 3s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.12, locked, ubuntu-latest)	46s
checks / test (3.10, lowest-direct, ubuntu-latest)	46s
checks / test (3.11, locked, ubuntu-latest)	43s
checks / test (3.11, locked, windows-latest)	1m 12s
checks / test (3.12, lowest-direct, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, windows-latest)	3m 7s
checks / test (3.13, locked, windows-latest)	1m 9s
checks / test (3.13, locked, ubuntu-latest)	42s
checks / test (3.12, locked, windows-latest)	1m 11s
checks / test (3.14, lowest-direct, windows-latest)	1m 15s
checks / test (3.14, locked, windows-latest)	1m 37s
checks / test (3.14, locked, ubuntu-latest)	1m 36s
checks / test (3.13, lowest-direct, windows-latest)	1m 10s
checks / test (3.13, lowest-direct, ubuntu-latest)	42s
checks / test (3.14, lowest-direct, ubuntu-latest)	34s
all-green	5s
	23m 31s

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