Python: Add Foundry Memory Context Provider (#3943)

* Initial plan

* Add FoundryMemoryProvider and tests

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

* Add sample and documentation for FoundryMemoryProvider

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* Address code review feedback for FoundryMemoryProvider

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* Address PR review comments: Add DEFAULT_SOURCE_ID, use logging.getLogger, move state to session.state

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

* Fix Foundry memory ItemParam usage and exports

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* Refactor provider hook state and standardize source IDs

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* Support endpoint-based Foundry memory init

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* updated implementation and sample

* updated code and samples

* Fix foundry memory provider tests: mock structure and field names

- Use Mock objects with memory_item.content for memory mocks
- Assert 'content' instead of 'text' on SDK message items
- Update exception types from ServiceInitializationError to ValueError
- Remove unused ServiceInitializationError import

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix mypy errors in foundry memory provider

Add type: ignore[arg-type] for scope (str | None vs str) and items
(list variance) passed to Azure SDK methods.

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* fix import

---------

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Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>
Co-authored-by: eavanvalkenburg <github@vanvalkenburg.eu>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docs/decisions/0016-python-context-middleware.md

@@ -1114,6 +1114,7 @@ Defaults introduced by this change:
 - `RedisContextProvider.DEFAULT_SOURCE_ID = "redis"`
 - `RedisHistoryProvider.DEFAULT_SOURCE_ID = "redis_memory"`
 - `AzureAISearchContextProvider.DEFAULT_SOURCE_ID = "azure_ai_search"`
+- `FoundryMemoryProvider.DEFAULT_SOURCE_ID = "foundry_memory"`
 
 
 ## Comparison to .NET Implementation