feat(mcpserver): let ToolError carry content for is_error results #3031

Job	Run time
checks / pre-commit	29s
checks / readme-snippets	14s
checks / test (3.14, lowest-direct, ubuntu-latest)	57s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.10, locked, ubuntu-latest)	1m 9s
checks / test (3.11, lowest-direct, ubuntu-latest)	56s
checks / test (3.10, locked, windows-latest)	1m 30s
checks / test (3.10, lowest-direct, windows-latest)	1m 49s
checks / test (3.11, lowest-direct, windows-latest)	1m 13s
checks / test (3.12, lowest-direct, windows-latest)	1m 42s
checks / test (3.14, locked, windows-latest)	2m 14s
checks / test (3.11, locked, ubuntu-latest)	1m 0s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 10s
checks / test (3.12, locked, windows-latest)	1m 32s
checks / test (3.12, locked, ubuntu-latest)	1m 10s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 3s
checks / test (3.11, locked, windows-latest)	1m 32s
checks / test (3.13, lowest-direct, windows-latest)	1m 10s
checks / test (3.13, locked, ubuntu-latest)	1m 0s
checks / test (3.14, locked, ubuntu-latest)	1m 40s
checks / test (3.14, lowest-direct, windows-latest)	1m 30s
checks / test (3.13, locked, windows-latest)	1m 32s
all-green	2s
	27m 35s

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