N function in pedigree sims

[hannesbecher]

When simulating pedigrees, one needs to set a population size N. This PR adds functionality for N to be a function of the generation (back in time). This works for forward and backward pedigree simulations.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.93%. Comparing base (e2932a2) to head (97f7f91).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2322   +/-   ##
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  Coverage   90.93%   90.93%           
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  Files          20       20           
  Lines       12014    12018    +4     
  Branches     2438     2439    +1     
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+ Hits        10925    10929    +4     
  Misses        602      602           
  Partials      487      487           

Flag	Coverage Δ
C	90.93% <100.00%> (+<0.01%)	⬆️
python	98.70% <100.00%> (+<0.01%)	⬆️

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[jeromekelleher]

LGTM - just needs some light test coverage I guess.

Some ideas:

• passing in population_size=lamba _: N should be identical to population_size=N
• passing in population_size=lamba t: 100 t < 10 else 1 should cause an immediate bottleneck at time 10

[hannesbecher]

LGTM - just needs some light test coverage I guess.

Some ideas:

* passing in `population_size=lamba _: N` should be identical to `population_size=N`

* passing in `population_size=lamba t: 100 t < 10 else 1` should cause an immediate bottleneck at time 10

I've tried. Do the added tests make sense?

[jeromekelleher]

Nice, just need to reformat the docstring style.

[jeromekelleher]

Can you reformat this using sphinx :param: sections like the rest of the code please?

[jeromekelleher]

Great! Can you squash down to one commit please? (See dev docs for guidance)

[hannesbecher]

NB, squashing is mentioned only in the tskit dev docs, I think.