Iterators dont inline

[blackmius]

Found that use of iterator which just extend field is cost additional 
computation time (about 20% time more)
    
    
     nim
    import std/[json, times, monotimes, tables]
    let a = %*{"a": 1, "b": 2, "c": 3}
    
    var start = getMonoTime()
    for i in 1..1_000_000:
      for k, v in a.fields.pairs:
        discard
    echo getMonoTime()-start
    
    start = getMonoTime()
    for i in 1..1_000_000:
      for k, v in a.pairs:
        discard
    echo getMonoTime()-start
    
    
    Run

but i dont see such effect when trying to simplify case
    
    
    iterator q1(): int =
      for i in 1..1_000_000:
        yield i
    
    iterator q2(): int =
      for i in q1():
        yield i
    
    var start = getMonoTime()
    for i in q1():
      discard
    echo getMonoTime()-start
    start = getMonoTime()
    for i in q2():
      discard
    echo getMonoTime()-start
    
    
    Run