fix(profiling): make sure lineno is always an int and funcname is never None

[jd]

In some cases, f_lineno can be None which would trigger an error in the pprof
output. This is not even caught by mypy, and I've proposed a fix here:

python/typeshed#6769

This patch makes sure we always use 0 if the line number is None.

It also makes sure a funcname is always passed — in practice it's now the case,
but make sure typing reflects that.

Fixes #3046

[P403n1x87]

Because unfortunately the f_lineno attribute can be 0 at times, the "correct" way of computing the line number is via f_lasti and f_code.co_lnotab. The details are in https://github.com/python/cpython/blob/main/Objects/lnotab_notes.txt. The annoying bit is that I believe the formula described there has changed a couple of times across releases.

[jd]

Because unfortunately the f_lineno attribute can be 0 at times, the "correct" way of computing the line number is via f_lasti and f_code.co_lnotab. The details are in https://github.com/python/cpython/blob/main/Objects/lnotab_notes.txt. The annoying bit is that I believe the formula described there has changed a couple of times across releases.

That's something we could improve in the future, though it does not impact this PR AFAICT.