Map ReasoningEffort.None and ExtraHigh to "none" and "xhigh" in OpenAI IChatClient implementations

[Copilot]

ReasoningEffort.None and ReasoningEffort.ExtraHigh were not mapping to their correct OpenAI API values. None was falling through to the wildcard default and mapping to null (indistinguishable from "not specified"), and ExtraHigh was mapping to High. Since ChatReasoningEffortLevel and ResponseReasoningEffortLevel are string-based extensible enum types, we construct new instances with the appropriate string values for cases where no static property is exposed.

Changes

• OpenAIChatClient.cs: Map ReasoningEffort.None → new ChatReasoningEffortLevel("none"), ReasoningEffort.ExtraHigh → new ChatReasoningEffortLevel("xhigh")
• OpenAIResponsesChatClient.cs: Map ReasoningEffort.None → new ResponseReasoningEffortLevel("none"), ReasoningEffort.ExtraHigh → new ResponseReasoningEffortLevel("xhigh")
• Tests: Added None/"none" and ExtraHigh/"xhigh" as [InlineData] on the existing parameterized theory tests

// Before: None fell through to _ => null, ExtraHigh mapped to High
// After:
effort switch
{
    ReasoningEffort.None => new ChatReasoningEffortLevel("none"),
    ReasoningEffort.Low => ChatReasoningEffortLevel.Low,
    ReasoningEffort.Medium => ChatReasoningEffortLevel.Medium,
    ReasoningEffort.High => ChatReasoningEffortLevel.High,
    ReasoningEffort.ExtraHigh => new ChatReasoningEffortLevel("xhigh"),
    _ => (ChatReasoningEffortLevel?)null,
};

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[Copilot]

Pull request overview

Updates OpenAI IChatClient implementations in Microsoft.Extensions.AI.OpenAI to correctly translate ReasoningEffort.None and ReasoningEffort.ExtraHigh to OpenAI API-compatible string values, and adjusts unit tests accordingly.

Changes:

• Map ReasoningEffort.None to "none" (instead of falling through to null) in both chat-completions and responses clients.
• Map ReasoningEffort.ExtraHigh to "xhigh" (instead of clamping to High) in both clients.
• Update OpenAI OpenAI test suites to validate the new JSON values via existing theory-based tests.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIChatClient.cs	Updates ReasoningEffort → ChatReasoningEffortLevel mapping for None/ExtraHigh.
src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs	Updates ReasoningEffort → ResponseReasoningEffortLevel mapping for None/ExtraHigh.
test/Libraries/Microsoft.Extensions.AI.OpenAI.Tests/OpenAIChatClientTests.cs	Adjusts theory data to expect "none"/"xhigh" for chat-completions request JSON.
test/Libraries/Microsoft.Extensions.AI.OpenAI.Tests/OpenAIResponseClientTests.cs	Adjusts theory data to expect "none"/"xhigh" for responses request JSON; removes an older fact test.