Add Python bindings for EPContext data callbacks (#32271)
### Description
<!-- Describe your changes. -->
Exposes stable named EPContext data read/write callbacks through Python.
- Provides allocator-backed read buffers, callback-scoped write views,
status propagation, GIL/reentrancy handling, and retained
session/compiler callback snapshots.
- Uses callback/state-only native registration. `max_data_size` is
retained and enforced by Python-owned callback state; no removed native
read-options API or native size-policy field is used.
- Tests retained buffer limits, exact-limit allocations, oversized
rejection, copied options, and callback ownership.
- Merges #32265 at `e0cc266cdefef4e27104b14e4091a9d61f75a214`, including
its main-branch update, retained-NHWC READ-support validation, and
provider-specific callback preflight before capability-time I/O.
- No additional Python callback signature change is required by this
refresh; capability preflight stays in the core runtime.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
This independent binding PR remains stacked on #32265. It enables
bounded, application-managed EPContext I/O without reintroducing payload
policy into the stable native transport ABI.
The latest core checks provider-specific callback requirements before
capability discovery, including AOT, NHWC, and ORT-format paths, rather
than relying solely on checks immediately before `Compile()`. Existing
Python callback failure and lifetime behavior is preserved.
Retarget to `main` after #32265 lands.
### Testing
Revalidated on Windows using the existing isolated Python environment:
- `cmake --build .\build\WindowsBindings\RelWithDebInfo --config
RelWithDebInfo --parallel 8 --target onnxruntime_pybind11_state
example_plugin_ep` — passed after merging `e0cc266cde`, including
regeneration for the updated core dependencies.
- Verified that the build's native/core/public-header/example-EP sources
match `e0cc266cde` and that Python imports the freshly rebuilt 1.31.0
module with the callback API present.
- From `build\WindowsBindings\RelWithDebInfo\RelWithDebInfo`, `python -m
pytest
C:\Users\gnallasamy\Codes\ort-bindings-471c3cdf\python\onnxruntime\test\python\onnxruntime_test_python_compile_api.py
-q` — 14 passed, 2 hardware-dependent skips.
- Scoped `ruff check`, `ruff format --check`, and `git diff --check
e0cc266cdefef4e27104b14e4091a9d61f75a214 HEAD` — passed.
The source-tree package emitted its expected missing
build/package-metadata warning. GPU/hardware-provider-specific preflight
paths and non-Windows runs were not performed.
---------
Co-authored-by: Gopalakrishnan Nallasamy <gopalakrishnan.nallasamy@microsoft.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Edward Chen <18449977+edgchen1@users.noreply.github.com>
