perf: discriminate JSONRPCMessage union by key presence instead of smart-union scoring #3546

Job	Run time
checks / pre-commit	52s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 18s
checks / test (3.11, locked, windows-latest)	2m 0s
checks / test (3.11, locked, ubuntu-latest)	1m 21s
checks / test (3.13, lowest-direct, windows-latest)	2m 0s
checks / test (3.12, locked, windows-latest)	1m 54s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 26s
checks / readme-snippets	15s
checks / test (3.12, locked, ubuntu-latest)	1m 44s
checks / test (3.10, locked, ubuntu-latest)	1m 36s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 28s
checks / test (3.11, lowest-direct, windows-latest)	1m 37s
checks / test (3.12, lowest-direct, windows-latest)	1m 53s
checks / test (3.10, lowest-direct, windows-latest)	1m 54s
checks / test (3.13, locked, windows-latest)	1m 40s
checks / test (3.13, locked, ubuntu-latest)	1m 16s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 33s
checks / docs	1m 8s
checks / test (3.10, locked, windows-latest)	1m 56s
checks / test (3.14, locked, ubuntu-latest)	1m 16s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 2s
checks / test (3.14, lowest-direct, windows-latest)	1m 53s
checks / test (3.14, locked, windows-latest)	1m 50s
all-green	2s
	34m 54s

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