[WIP] feat: add Accumulator

[kohlisid]

Fixes: #219

[codecov]

Codecov Report

Attention: Patch coverage is 0.77720% with 383 lines in your changes missing coverage. Please review.

Project coverage is 81.05%. Comparing base (6ccd49e) to head (67f5e87).

Files with missing lines	Patch %	Lines
pynumaflow/accumulator/_dtypes.py	0.00%	186 Missing ⚠️
pynumaflow/accumulator/servicer/task_manager.py	0.00%	124 Missing ⚠️
pynumaflow/accumulator/servicer/async_servicer.py	0.00%	37 Missing ⚠️
pynumaflow/accumulator/async_server.py	0.00%	33 Missing ⚠️
pynumaflow/accumulator/__init__.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #223       +/-   ##
===========================================
- Coverage   94.19%   81.05%   -13.14%     
===========================================
  Files          58       63        +5     
  Lines        2359     2745      +386     
  Branches      119      143       +24     
===========================================
+ Hits         2222     2225        +3     
- Misses        100      483      +383     
  Partials       37       37               

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