[taegyunkim]

Implements the proposal in gh-160107.

• _PyRuntimeState gets a new asyncio_debug_offsets pointer, and its offset is published as _Py_DebugOffsets.runtime_state.asyncio_debug_offsets. _asyncio's module init stores &_Py_AsyncioDebug there with a release store. It is NULL until _asyncio is initialized.
• Py_AsyncioModuleDebugOffsets now starts with a cookie ("xasyncpy"), PY_VERSION_HEX and its size. The AsyncioDebug section is kept.
• _remote_debugging follows the pointer instead of searching loaded binaries for the section, and rejects a table whose cookie doesn't match, whose version differs from _Py_DebugOffsets.version, or whose size is smaller than the local struct. The new runtime-state field is added to the validation list and the static_assert sizes are updated.
• New test in test_external_inspection that follows the pointer from _PyRuntime with ctypes: NULL before import _asyncio, then a valid header after.

Tested on Linux arm64 (test_external_inspection, test_profiling, test_capi, with ptrace allowed so the remote asyncio tests run) and on a macOS arm64 debug build, where the remote-inspection tests skip without root. Not tested on Windows yet.

I used AI to help write this change. I have reviewed all of it.

[taegyunkim]

This is a reference implementation for gh-160107. I opened it earlier than I meant to, before the issue had any discussion, and I'm sorry for the CI it triggered. If a triager can cancel the queued run, please do. I won't push again until there's agreement on the direction in the issue.