[NKIFE-415] print assert messages

[ppotapov-aws]

Trace fun things like:

def f():
  print("Here we go again")
  assert 2 + 2 == 5, f"Some fun math you do, huh. Should be {2 + 2}"

Produces

Here we go again

/Users/ppotapov/work/KLR/./test.py:26:
  assert 2 + 2 == 5, f"Some fun math you do, huh. Should be {2 + 2}"
   ^-- assertion failed, Some fun math you do, huh. Should be 4
Traceback (most recent call last):
  File "/Users/ppotapov/work/KLR/./test.py", line 62, in <module>
    t.trace()
  File "/Users/ppotapov/work/KLR/./test.py", line 57, in trace
    raise Exception("tracing error")
Exception: tracing error

[govereau]

Great, thanks!