.NET: Allow storage of auto-approved functions

[westey-m]

Motivation and Context

When we have functions that require approval, and those that do not, and a mixture of the two need to be executed at the same time, we ask for approval for both, since we have no-where to store the results.
With the availability of ambient agent/session state, we can now use Agent specific ChatClient middleware to store the ones that don't require approval in the session, to avoid sending them to the user.

#4909
#6264

Description

• Add a ChatClient decorator to store approved functions, so we don't ask the user to approve something that doesn't require approval

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

Adds a new chat-client middleware layer to support mixed tool-approval scenarios by hiding “auto-approvable” approval requests from the user while preserving them in session state for automatic approval on the next turn.

Changes:

• Introduces AutoApprovedFunctionRemovingChatClient to filter/store auto-approvable ToolApprovalRequestContent and re-inject them as approved on the next request.
• Wires the decorator into the default ChatClientAgent pipeline behind a new ChatClientAgentOptions.StoreAutoApprovedFunctionCalls flag (and adds a builder extension for custom stacks).
• Adds unit tests covering non-streaming and streaming filtering/storage/injection behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI/ChatClient/AutoApprovedFunctionRemovingChatClient.cs	New decorator that stores auto-approvable approval requests in session and re-injects them as approved responses.
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientExtensions.cs	Injects the new decorator into the default middleware pipeline when the new option is enabled.
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientBuilderExtensions.cs	Adds UseAutoApprovedFunctionRemoval() for custom chat client stacks.
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentOptions.cs	Adds StoreAutoApprovedFunctionCalls option and clones it.
dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/AutoApprovedFunctionRemovingChatClientTests.cs	New unit tests validating filtering, storage, and injection behavior.