Raise errors for uncaught FutureWarnings / DeprecationWarnings in signac.

[bdice]

Description

To help ensure that all DeprecationWarnings are converted to FutureWarnings, I updated our pytest configuration to treat warnings as errors. I added exceptions for all existing warnings.

Merging this PR will help us identify all DeprecationWarnings that should be replaced by FutureWarnings. We will remove all existing exceptions for DeprecationWarning in setup.cfg and the test files as they are converted to FutureWarning.

Motivation and Context

Aids with #687. This can be merged before #718 but it will require modifications to setup.cfg after that PR is merged.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• The package documentation and framework documentation in signac-docs are up to date with these changes.
• I have updated the changelog and added any related issue and pull request numbers for future reference.

[codecov]

Codecov Report

Merging #713 (4ce7625) into master (3cd249c) will decrease coverage by 0.06%.
The diff coverage is n/a.

❗ Current head 4ce7625 differs from pull request most recent head 39599f7. Consider uploading reports for the commit 39599f7 to get more accurate results

@@            Coverage Diff             @@
##           master     #713      +/-   ##
==========================================
- Coverage   78.34%   78.27%   -0.07%     
==========================================
  Files          66       66              
  Lines        7231     7231              
  Branches     1586     1586              
==========================================
- Hits         5665     5660       -5     
- Misses       1251     1255       +4     
- Partials      315      316       +1     

Impacted Files	Coverage Δ
signac/common/deprecation/__init__.py	62.22% <0.00%> (-2.23%)	⬇️
signac/__main__.py	71.33% <0.00%> (-0.34%)	⬇️
signac/cite.py	50.00% <0.00%> (ø)
signac/syncutil.py	76.39% <0.00%> (ø)
signac/core/json.py	86.66% <0.00%> (ø)
signac/common/host.py	40.42% <0.00%> (ø)
signac/contrib/job.py	90.64% <0.00%> (ø)
signac/db/database.py	100.00% <0.00%> (ø)
signac/common/crypt.py	64.00% <0.00%> (ø)
signac/core/utility.py	72.22% <0.00%> (ø)
... and 7 more

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[csadorf]

One question, but looks good overall.