Add AGENTS.md and GitHub Copilot instructions #651

Job	Run time
build_linux (3.10, 2.2)	2m 54s
build_windows (3.10, 2.2)	7m 24s
build_windows (3.13, 2.3)	6m 58s
build_linux (3.11, 2.3)	2m 58s
build_windows (3.11, 2.3)	16m 8s
build_linux (3.13, 2.3)	2m 54s
build_linux (3.12, 2.3)	2m 49s
build_windows (3.12, 2.3)	10m 55s
test_linux (3.12, numpy">=2", false, ubuntu-latest)	2m 23s
test_linux (3.10, numpy">=2", false, ubuntu-latest)	1m 46s
test_linux (3.13, numpy">=2", false, ubuntu-latest)	1m 43s
test_linux (3.11, numpy">=2", false, ubuntu-latest)	1m 54s
test_windows (3.13, numpy">=2", false, windows-latest)	3m 15s
test_windows (3.12, numpy">=2", false, windows-latest)	3m 13s
test_windows (3.11, numpy">=2", false, windows-latest)	3m 29s
test_windows (3.10, numpy">=2", false, windows-latest)	3m 16s
	1h 13m 59s

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