sketch: refactor lowlevel server to handler pattern #433

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	32s
checks / test (3.12, lowest-direct, windows-latest)	6m 40s
checks / test (3.10, locked, windows-latest)	6m 47s
checks / test (3.10, lowest-direct, windows-latest)	6m 45s
checks / test (3.12, lowest-direct, ubuntu-latest)	6m 13s
checks / test (3.10, locked, ubuntu-latest)	6m 8s
checks / test (3.11, lowest-direct, ubuntu-latest)	7m 21s
checks / test (3.11, lowest-direct, windows-latest)	6m 24s
checks / test (3.11, locked, windows-latest)	6m 27s
checks / test (3.13, lowest-direct, ubuntu-latest)	5m 53s
checks / test (3.11, locked, ubuntu-latest)	7m 22s
checks / test (3.13, locked, ubuntu-latest)	7m 21s
checks / test (3.10, lowest-direct, ubuntu-latest)	7m 21s
checks / test (3.12, locked, ubuntu-latest)	7m 30s
checks / test (3.14, locked, windows-latest)	7m 11s
checks / test (3.13, locked, windows-latest)	6m 20s
checks / test (3.14, lowest-direct, ubuntu-latest)	7m 26s
checks / test (3.13, lowest-direct, windows-latest)	6m 21s
checks / test (3.14, locked, ubuntu-latest)	8m 30s
checks / test (3.12, locked, windows-latest)	6m 31s
checks / test (3.14, lowest-direct, windows-latest)	6m 19s
all-green	5s
	2h 17m 40s

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