fix(OpenAI): default missing optional keys to null in from()

[lazerg]

What:

• Bug Fix
• New Feature

Description:

WebSearchUserLocation::from() and OutputMcpCall::from() read their nullable keys straight from $attributes, so a response that omits those optional keys triggers an "Undefined array key" warning. This defaults them to null with ?? null, the same way the other from() methods already handle optional keys.

Related:

fixes: #781

[iBotPeaches]

Any further context on the set_error_handler usage? None of our other tests do that, so curious what you hit or trying to test with that.

[lazerg]

Undefined array key only warns in PHP, doesn't throw. Value's null either way, so a plain assertion wouldn't catch the regression without escalating it. Scoped to that one call via try/finally so it doesn't leak into other tests.