draft: MRTR (SEP-2322) lowlevel plumbing + handler-shape comparison #1557

Job	Run time
checks / pre-commit	31s
checks / readme-snippets	14s
checks / test (3.11, lowest-direct, ubuntu-latest)	53s
checks / test (3.11, lowest-direct, windows-latest)	2m 39s
checks / test (3.10, locked, ubuntu-latest)	54s
checks / test (3.10, lowest-direct, windows-latest)	2m 22s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.12, lowest-direct, ubuntu-latest)	57s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.14, locked, ubuntu-latest)	2m 14s
checks / test (3.10, locked, windows-latest)	2m 11s
checks / test (3.12, locked, windows-latest)	3m 11s
checks / test (3.12, lowest-direct, windows-latest)	3m 19s
checks / test (3.13, lowest-direct, windows-latest)	2m 36s
checks / test (3.13, lowest-direct, ubuntu-latest)	56s
checks / test (3.11, locked, windows-latest)	2m 24s
checks / test (3.13, locked, windows-latest)	2m 17s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 15s
checks / test (3.12, locked, ubuntu-latest)	54s
checks / test (3.14, lowest-direct, windows-latest)	2m 4s
checks / test (3.13, locked, ubuntu-latest)	45s
checks / test (3.14, locked, windows-latest)	2m 47s
all-green	5s
	37m 18s

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