Improve task execution and testing in goPool

[daniel-hutao]

• Modified the executeTaskWithTimeout function in worker.go to stop the task when the context is cancelled.
• Updated the Wait function in gopool.go to wait until all tasks are completed, not just dispatched.
• Added a new test case TestGoPoolWithTimeout in gopool_test.go to test the behavior of goPool when a task times out.
• Used the existing lock field in goPool to protect concurrent access to workerStack in Wait and popWorker functions.

fix #6