Don't access loop variables in goroutines directly

[guggero]

Inspired by #7186.
I checked all anonymous goroutines to make sure they don't access any loop or other temporary variables.
This PR fixes the found instances and also contains some readability improvements to visually highlight defer statements better.

[bhandras]

Nice!!

[Crypt-iQ]

I think the ones that don't iterate in a for loop are fine - see comment #7186 (comment)

[yyforyongyu]

I think @Crypt-iQ is correct and sorry that I gave the wrong reason to make this change🙈

Nonetheless, I find using an anonymous goroutine inside a select statement wrapped in a for loop can be very error-prone, as we are secretly accessing variables inside a loop and may cause the bug. So although the reason is wrong in the first place, I still think it's a better pattern to pass variables into the anonymous functions so we don't need to raise such a concern. Or, even better, avoid using anonymous goroutines, which can also benefit our unit tests.

I think the original post said it well,

One of these two changes is unnecessary and the other is a real bug fix, but you can’t tell which is which without more context.

[guggero]

I think the ones that don't iterate in a for loop are fine.

I agree after taking a look at your code examples in the referenced PR. I also wasn't sure if the type conversion of the switch already put things on the stack. But I still feel like this more explicit version also puts more emphasis on the goroutine using a variable from outside of its context. So I'm going to merge this anyway.