Add custom content support to ToolError for isError responses #3969

Job	Run time
checks / pre-commit	40s
checks / readme-snippets	11s
checks / test (3.10, highest, windows-latest)	2m 18s
checks / test (3.10, lowest-direct, ubuntu-latest)	45s
checks / test (3.10, lowest-direct, windows-latest)	2m 20s
checks / test (3.11, highest, windows-latest)	2m 32s
checks / test (3.10, highest, ubuntu-latest)	44s
checks / test (3.11, lowest-direct, ubuntu-latest)	44s
checks / test (3.11, highest, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, windows-latest)	2m 44s
checks / test (3.13, lowest-direct, ubuntu-latest)	42s
checks / test (3.11, lowest-direct, windows-latest)	2m 25s
checks / test (3.13, highest, windows-latest)	2m 22s
checks / test (3.13, highest, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, ubuntu-latest)	47s
checks / test (3.12, highest, windows-latest)	3m 39s
checks / test (3.12, highest, ubuntu-latest)	1m 8s
checks / test (3.12, lowest-direct, windows-latest)	3m 23s
	28m 58s

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