added update_parents flag and set default values for arity in selection operators

[itaitzruia4]

For memory efficiency, Individual now has a field update_parents to only update parents optionally.

[itaitzruia4]

should be merged after #104

[achiyae]

@itaitzruia4 I don't like this PR. By its name, it seems like it's only adding a flag, but there are 53 file changes!
Also, when I look at the changes, it's doing way more than adding a flag...

[itaitzruia4]

Re-opening to run examples workflow too

[itaitzruia4]

@itaitzruia4 I don't like this PR. By its name, it seems like it's only adding a flag, but there are 53 file changes! Also, when I look at the changes, it's doing way more than adding a flag...

It's been a while since I wrote this code, but it looks like most of the changes are due to format fixes.
The actual changes are update_parents flag (which requires a change in many files as you mentioned), and setting a default value for arity field in Selection operators (number of individuals to be selected).