Fix notifications

[x42005e1f]

What do these changes do?

This PR fixes hang in AsyncQueue.join() by replacing asyncio.Event with asyncio.Condition. It also:

1. Makes the names of primitives the same style.
2. Reduces notifications in Reduce notifications for a minor speedup #704 style.
3. Ensures that counters are changed exclusively.

Are there changes in behavior for the user?

There are no behavior changes for users.

Related issue number

Fixes #715

[codspeed-hq]

CodSpeed Performance Report

Merging #716 will degrade performances by 28.08%

_{Comparing x42005e1f:master (e3a8eba) with master (f90a38a)}

Summary

❌ 1 (👁 1) regressions
✅ 3 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	x42005e1f:master	Change
👁	test_bench_sync_put_async_join	256.1 ms	356.1 ms	-28.08%

[codecov]

Codecov Report

Attention: Patch coverage is 95.31250% with 3 lines in your changes missing coverage. Please review.

Project coverage is 94.18%. Comparing base (f90a38a) to head (e3a8eba).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
janus/__init__.py	95.31%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #716      +/-   ##
==========================================
- Coverage   94.49%   94.18%   -0.32%     
==========================================
  Files           5        5              
  Lines        1490     1495       +5     
  Branches      131      135       +4     
==========================================
  Hits         1408     1408              
- Misses         53       54       +1     
- Partials       29       33       +4     

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