Fix deprecations

[allt0ld]

Description

• Added get_event_loop to curvesim.utils, replacing usage of asyncio.get_event_loop across various files, to avoid DeprecationWarning (which will become an error in the future) raised when you call asyncio.get_event_loop without a running/set event loop.
• Replaced deprecated license_file setup.cfg param with license_files.

Resolves #160, resolves #157.

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

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[github-actions]

Coverage report

The coverage rate went from 75.16% to 75.04% ⬇️
The branch rate is 61%.

100% of new lines are covered.

Diff Coverage details (click to unfold)

curvesim/pool_data/queries.py

100% of new lines are covered (85% of the complete file).

curvesim/utils.py

100% of new lines are covered (74.68% of the complete file).

curvesim/network/utils.py

100% of new lines are covered (79.59% of the complete file).