Fix arbitrary memory read (#29011)
This pull request strengthens security around loading ONNX models by
adding a defense-in-depth check that rejects Constant nodes with dense
tensor attributes referencing internal ORT in-memory address markers. It
also introduces a regression test to ensure this attack vector is
blocked.
**Security hardening:**
* Added an explicit check in `ConstantNodeProtoToTensorProto` to reject
Constant node tensor attributes with ORT in-memory address markers,
preventing crafted models from propagating unsafe pointers.
**Testing:**
* Added a regression test
`RejectInMemoryMarkerOnConstantNodeTensorAttribute` to verify that
models containing Constant nodes with such in-memory markers are
rejected during model load.
