Added tox support for local testing

[s3rius]

This PR adds support for tox to easily test against different python environments easily.

Ref: #164 (comment)

[codecov-commenter]

Codecov Report

Merging #166 (2b43240) into develop (e66f3aa) will increase coverage by 0.20%.
The diff coverage is 70.76%.

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@@             Coverage Diff             @@
##           develop     #166      +/-   ##
===========================================
+ Coverage    67.62%   67.82%   +0.20%     
===========================================
  Files           37       45       +8     
  Lines          942     1380     +438     
===========================================
+ Hits           637      936     +299     
- Misses         305      444     +139     

Impacted Files	Coverage Δ
taskiq/abc/middleware.py	100.00% <ø> (ø)
taskiq/abc/result_backend.py	100.00% <ø> (ø)
taskiq/cli/scheduler/run.py	0.00% <0.00%> (ø)
taskiq/cli/watcher.py	0.00% <ø> (ø)
taskiq/cli/worker/log_collector.py	100.00% <ø> (ø)
taskiq/cli/worker/process_manager.py	0.00% <0.00%> (ø)
taskiq/cli/worker/run.py	0.00% <0.00%> (ø)
taskiq/events.py	100.00% <ø> (ø)
taskiq/result/v1.py	0.00% <0.00%> (ø)
taskiq/result_backends/dummy.py	100.00% <ø> (ø)
... and 26 more

... and 1 file with indirect coverage changes

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