test(showcase): add integration tests showing LRO drops error details

[nnicolee]

This PR adds two new integration test cases to the gapic-showcase client targeting LRO error scenarios:

• testGRPC_LROErrorResponse_dropsErrorDetails
• testHttpJson_LROErrorResponse_dropsErrorDetails

These tests reproduce the defect described in #13369. They configure the showcase LRO Wait endpoint to fail with structured error details (a gRPC Status with packed PoetryError details) and assert that under the current code generator output, the thrown ApiException.getErrorDetails() returns null for both transports.

These test cases serve as a baseline showcase to demonstrate the issue. Once the planned generator changes are implemented, we will update these test cases to assert that the structured error details are correctly parsed and populated inside getErrorDetails().

[gemini-code-assist]

Code Review

This pull request adds integration tests to verify that error details are currently dropped during LRO error parsing for both gRPC and HTTP/JSON clients. The reviewer recommends adding a timeout to the operationFuture.get() calls in both tests to prevent potential indefinite hangs in CI.

[gemini-code-assist]

Calling operationFuture.get() without a timeout can cause the test to hang indefinitely in CI if there is a regression or bug where the future never completes. It is safer to specify a timeout to ensure the test fails fast.

Suggested change

	ExecutionException exception =
	assertThrows(ExecutionException.class, operationFuture::get);
	ExecutionException exception =
	assertThrows(ExecutionException.class, () -> operationFuture.get(10, TimeUnit.SECONDS));

[gemini-code-assist]

Calling operationFuture.get() without a timeout can cause the test to hang indefinitely in CI if there is a regression or bug where the future never completes. It is safer to specify a timeout to ensure the test fails fast.

Suggested change

	ExecutionException exception =
	assertThrows(ExecutionException.class, operationFuture::get);
	ExecutionException exception =
	assertThrows(ExecutionException.class, () -> operationFuture.get(10, TimeUnit.SECONDS));