Allow creating janus.Queue without running asyncio loop

[asvetlov]

Closes #448

[codspeed-hq]

CodSpeed Performance Report

Merging #710 will not alter performance

_{Comparing no-loop (c38e30e) with master (b1e6e0f)}

Summary

✅ 4 untouched benchmarks

[codecov]

Codecov Report

Attention: Patch coverage is 97.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.54%. Comparing base (b1e6e0f) to head (c38e30e).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
janus/__init__.py	96.49%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #710      +/-   ##
==========================================
+ Coverage   94.42%   94.54%   +0.11%     
==========================================
  Files           5        5              
  Lines        1472     1504      +32     
  Branches      127      131       +4     
==========================================
+ Hits         1390     1422      +32     
+ Misses         55       53       -2     
- Partials       27       29       +2     

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