Refactor EPContext data callbacks for EP-owned I/O

[GopalakrishnanN]

Summary:

• replace OrtEpApi EPContext read/write helper APIs with callback getter APIs so EPs own file/mmap fallback behavior
• add an Ort::EpContextConfig RAII wrapper and update the example plugin EP to use it
• bump the new API surface to ORT API version 28 and update focused EPContext tests

Validation:

• lintrunner -a on touched files: passed
• built onnxruntime_test_all: passed
• built onnxruntime_autoep_test: passed
• onnxruntime_test_all.exe --gtest_filter=PluginExecutionProviderTest.EpContext*: 6 tests passed
• onnxruntime_autoep_test.exe --gtest_filter=OrtEpLibrary.EpContext: 9 tests passed
• onnxruntime_autoep_test.exe: 59 tests passed

[Copilot]

Pull request overview

Refactors EPContext data I/O so execution providers can retrieve user-provided read/write callbacks (and associated state) from an opaque OrtEpContextConfig, allowing EP-owned fallback behavior for file/mmap handling.

Changes:

• Bumps ORT version/API surface to 1.28.0 / ORT_API_VERSION 28 and adds new C/C++ APIs for EPContext data callbacks.
• Introduces OrtEpContextConfig in the EP API to extract and later retrieve EPContext read/write callbacks from session/compile options.
• Updates the example plugin EP and focused EPContext tests to validate callback plumbing for embedded vs external EPContext data.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
VERSION_NUMBER	Bump runtime version to 1.28.0.
onnxruntime/test/framework/ep_plugin_provider_test.cc	Adds unit tests for EPContext config/callback accessors and argument validation.
onnxruntime/test/autoep/test_execution.cc	Adds AutoEP coverage for external EPContext data using read/write callbacks.
onnxruntime/test/autoep/library/example_plugin_ep/ep.h	Extends example EP config and plumbs Ort::EpContextConfig ownership into EP instance.
onnxruntime/test/autoep/library/example_plugin_ep/ep.cc	Implements callback-or-file fallback logic for EPContext external data; writes external EPContext via callback when provided.
onnxruntime/test/autoep/library/example_plugin_ep/ep_factory.cc	Extracts OrtEpContextConfig during EP creation and passes it to the EP.
onnxruntime/core/session/plugin_ep/ep_api.h	Declares new EP API entrypoints for EPContext config + callback getters.
onnxruntime/core/session/plugin_ep/ep_api.cc	Implements EPContext config handle and callback getter APIs; appends to OrtEpApi.
onnxruntime/core/session/ort_apis.h	Adds declaration for SessionOptions_SetEpContextDataReadFunc in the core API surface.
onnxruntime/core/session/onnxruntime_c_api.cc	Bumps internal OrtApi struct instance to ort_api_1_to_28 and appends new API function pointer.
onnxruntime/core/session/model_compilation_options.h	Adds ModelCompilationOptions::SetEpContextDataWriteFunc.
onnxruntime/core/session/model_compilation_options.cc	Stores EPContext write callback into model generation options.
onnxruntime/core/session/compile_api.h	Adds compile API entrypoint for setting EPContext data write callback.
onnxruntime/core/session/compile_api.cc	Implements compile API entrypoint and appends it to OrtCompileApi.
onnxruntime/core/session/abi_session_options.cc	Implements SessionOptions_SetEpContextDataReadFunc storage.
onnxruntime/core/framework/session_options.h	Adds storage for EPContext read callback + state in internal SessionOptions.
onnxruntime/core/framework/ep_context_options.h	Adds EpContextDataWriteFuncHolder to model generation options.
onnxruntime/core/framework/ep_context_options.cc	Adds accessor to retrieve EPContext write callback holder.
include/onnxruntime/core/session/onnxruntime_ep_c_api.h	Public EP API additions: OrtEpContextConfig handle + callback getter APIs.
include/onnxruntime/core/session/onnxruntime_cxx_inline.h	Adds inline C++ wrappers for Ort::EpContextConfig and new setter wrappers.
include/onnxruntime/core/session/onnxruntime_cxx_api.h	Declares Ort::EpContextConfig RAII wrapper and new SessionOptions/ModelCompilationOptions methods.
include/onnxruntime/core/session/onnxruntime_c_api.h	Bumps ORT_API_VERSION to 28 and adds callback typedefs + new C/Compile API functions.

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