Add a new SQLiteBucket subclass that uses py-filelock

[JWCook]

Fixes #67 and #60

The changes in #61 made SQLiteBucket safe to use with multiple threads, and multiple processes with a shared Limiter.

However, to work with multiple processes without a shared Limiter, a different means of inter-process communication is needed. A file lock seems to be the best way to do this. This does reduce performance, and also requires an extra dependency, so I'm making a separate bucket class for this.

Changes

• Added FileLockSQLiteBucket
• Added a test using multiple processes without a shared Limiter
• Bumped LimitContextDecorator log messages down to debug, as it gets a bit spammy during the longer tests (with pytest -v -s)
• Added backend dependencies as optional extras in poetry.dependencies and poetry.extras
  • This does not cause these these dependencies to be installed by default, but adds them to package metadata
  • Also makes them installable via poetry install -E all or pip install pyrate-limiter[all]

[codecov]

Codecov Report

Merging #68 (49392ad) into master (eda4d07) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #68      +/-   ##
==========================================
+ Coverage   97.95%   98.06%   +0.11%     
==========================================
  Files           8        8              
  Lines         342      362      +20     
  Branches       32       32              
==========================================
+ Hits          335      355      +20     
  Misses          4        4              
  Partials        3        3              

Impacted Files	Coverage Δ
pyrate_limiter/limit_context_decorator.py	100.00% <100.00%> (ø)
pyrate_limiter/sqlite_bucket.py	100.00% <100.00%> (ø)

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