Fix race condition in ContainersService.create()

[bismansahni]

Summary

Fixes #692

This PR resolves a race condition in ContainersService.create() that occurs when creating containers with the same name concurrently.

Changes

• Wrapped the entire create() method body with lock.withLock to ensure atomic container creation
• Added proper await keywords for actor isolation when accessing self.containers within the lock closure
• Changed direct container state assignment to use setContainerState() with context

Problem

Without the lock, two concurrent create() calls could both pass the existence check at line 133 and proceed to create the same container directory, resulting in filesystem errors like:

Error Domain=NSCocoaErrorDomain Code=516 "vmlinux-6.12.28-153 couldn't be copied to test-race because an item with the same name already exists."

Solution

By wrapping the entire method with lock.withLock, only one container creation can proceed at a time. The second concurrent call will now properly receive:

Error: internalError: "failed to create container" (cause: "exists: "container already exists: test-race"")

This follows the same pattern used in other methods like bootstrap(), startProcess(), and delete().

Testing

• All existing tests pass (make test)
• Code compiles successfully (swift build)
• The fix can be verified using the reproduction script from issue [Bug]: Race conditions in ContainersService #692

[dkovba]

@bismansahni Thank you for the contribution!

Should we do the same in the methods below?

• createProcess()
• stop()
• delete()
• _cleanup()