Simplify code by using Flow methods __len__ and __getitem__

[janosh]

Saves accessing flow.jobs a bunch.

[codecov]

Codecov Report

Merging #467 (7c66385) into main (85aabc5) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #467   +/-   ##
=======================================
  Coverage   99.86%   99.86%           
=======================================
  Files          20       20           
  Lines        1516     1516           
  Branches      419      419           
=======================================
  Hits         1514     1514           
  Misses          2        2           

Files	Coverage Δ
src/jobflow/core/flow.py	100.00% <100.00%> (ø)
src/jobflow/utils/graph.py	100.00% <100.00%> (ø)

[utf]

Hi @janosh, please could you revert this change, since it overlaps with the __getitem__ stuff proposed in #450. The __len__ part should still be fine.

At some point, we will need to rewrite the __getitem__ stuff in Flow and so with this PR we'd have to rewrite all the tests too.

[janosh]

could you specify what you mean by "have to rewrite the Flow.getitem"? do you want to make it behave like a dict rather than a list of jobs?