Avoid @_implicitSelfCapture pitfall by always adding `[weak self]` in `Task.init` closure

avoid-implicitSelfCapture.swift

// Always use `[weak self]` explicitly here to prevent `self` from being retained until the end of Task scope.
//
// NOTE: 
// Because of `Task.init` having `@_implicitSelfCapture` by (bad) API design, 
// without `[weak self]` will cause implicit strong `self` reference, which may never get deallocated
// especially when using `for await`.
//
// See also: https://twitter.com/inamiy/status/1544252986339504128
Task { [weak self] in
    for await x in sequence {
    	...
    	// With `[weak self]`, there is a chance of `self` getting deallocated in the mid of for-await loop.
    }
    
    // Without `[weak self]`, `self` is kept retained until the end of async scope.
    // If `for await` is never-ending stream, `self` will never be deallocated!
}