max short fixes

[dpaiton]

Resolved Issues

Partially addresses #121 & #136

Description

These changes arose in my other pr (#116) while trying to debug issues and high tolerances in short::max. There are a lot of commits in order to separate out meaningful changes from trivial ones. A majority of the changes are code reorganization, docstring fixes, and some additional sanity checks.

Major changes were:

• fuzz_calculate_max_short

  • was renamed to more accurately reflect what it is testing -- max short in the budget constrained regime
  • was rewritten to ensure the budget is constrained. I believe the reason the failures were "intermittent" before was because it was not always hitting the failure case. It hits it a lot now.
  • the tolerance was updated so that it consistently passes, to give us an idea of how much it is off from what we want.

• calculate_max_short
  this code was incorrect:

         let absolute_max_deposit =
           match self.calculate_open_short(max_bond_amount, open_vault_share_price) {
               Ok(d) => d,
               Err(_) => return Ok(max_bond_amount),

we do not want to return the bond amount if calculate_open_short is throwing an error. I updated it.

I ran the tests locally with FUZZ_RUNS=1_000 and FAST_FUZZ_RUNS=50_000 without any tests failing.

[jalextowle]

LGTM