Enable _tweak_price for 3-coin Cryptopools

[allt0ld]

Description

• Made minor changes to CurveCryptoPool._tweak_price like changing parameter types and adding a few error messages.
• Most of the lines come from the new test_tweak_price function in test_tricrypto.py, which tests _tweak_price's behavior after a pool experiences donations, an exchange, a deposit, and a withdrawal.

Hygiene checklist

• Changelog entry
• Everything public has a Numpy-style docstring
  (modules, public functions, classes, and public methods)
• Commit history is cleaned-up with minor changes squashed together
  and descriptive commit messages following Tim Pope's style

Cute Animal Picture

[github-actions]

Coverage report

The coverage rate went from 78.2% to 78.33% ⬆️
The branch rate is 64%.

92.3% of new lines are covered.

Diff Coverage details (click to unfold)

curvesim/pool/cryptoswap/pool.py

92.3% of new lines are covered (90.3% of the complete file).
Missing lines: 383, 422