[3.14] gh-148178: Validate remote debug offset tables on load (GH-148187) (#148577)

[3.14] gh-148178: Validate remote debug offset tables on load (GH-148187) (#148577)

Treat the debug offset tables read from a target process as untrusted input
and validate them before the unwinder uses any reported sizes or offsets.

Add a shared validator in debug_offsets_validation.h and run it once when
_Py_DebugOffsets is loaded and once when AsyncioDebug is loaded. The checks
cover section sizes used for fixed local buffers and every offset that is
later dereferenced against a local buffer or local object view. This keeps
the bounds checks out of the sampling hot path while rejecting malformed
tables up front.
(cherry picked from commit 289fd2c97a7e5aecb8b69f94f5e838ccfeee7e67)