Return `CallToolResult` from `convert_result` instead of a tuple #960

Job	Run time
checks / readme-snippets	16s
checks / pre-commit	30s
checks / test (3.10, locked, ubuntu-latest)	50s
checks / test (3.11, lowest-direct, ubuntu-latest)	57s
checks / test (3.10, locked, windows-latest)	2m 14s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, windows-latest)	2m 17s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.11, lowest-direct, windows-latest)	2m 42s
checks / test (3.13, locked, ubuntu-latest)	45s
checks / test (3.13, lowest-direct, ubuntu-latest)	55s
checks / test (3.11, locked, windows-latest)	2m 30s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 17s
checks / test (3.12, lowest-direct, windows-latest)	3m 59s
checks / test (3.13, lowest-direct, windows-latest)	2m 33s
checks / test (3.13, locked, windows-latest)	2m 19s
checks / test (3.12, locked, windows-latest)	3m 39s
checks / test (3.14, lowest-direct, windows-latest)	2m 32s
checks / test (3.12, locked, ubuntu-latest)	53s
checks / test (3.14, locked, ubuntu-latest)	2m 23s
checks / test (3.14, locked, windows-latest)	3m 12s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 0s
all-green	3s
	39m 37s

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