Fix VerifySessionNotFoundStatistics test for exception-less 404/1002 responses

[Copilot]

The VerifySessionNotFoundStatistics test expects ReadItemAsync<T> to throw CosmosException for session-not-found errors (404/1002), but exception-less behavior is now enabled by default.

Changes

• CosmosItemTests.cs: Updated test to validate response status codes instead of catching exceptions
  • Assert HttpStatusCode.NotFound and SubStatusCodes.ReadSessionNotAvailable on response
  • Verify diagnostics contain "Point Operation Statistics"
  • Removed try-catch block expecting exception

Before (exception-based):

try {
    await container.ReadItemAsync<ToDoActivity>(id, pk, 
        new ItemRequestOptions() { SessionToken = staleToken });
    Assert.Fail("Should have thrown");
} catch (CosmosException ex) {
    Assert.AreEqual(StatusCodes.NotFound, ex.StatusCode);
    // ...
}

After (exception-less):

var response = await container.ReadItemAsync<ToDoActivity>(id, pk,
    new ItemRequestOptions() { SessionToken = staleToken });
    
Assert.AreEqual(HttpStatusCode.NotFound, response.StatusCode);
Assert.AreEqual(SubStatusCodes.ReadSessionNotAvailable, response.Headers.SubStatusCode);
Assert.IsTrue(response.Diagnostics.ToString().Contains("Point Operation Statistics"));

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[kirankumarkolli]

Duplicate of #5756