Complete itertools.chain interface

[maxfischer2781]

This PR adjusts the itertools.chain class to provide similar functionality as before. Major changes include:

• Added an aclose method (closes Change in behavior of chain() between 3.10.5 and 3.10.6. #107)
• Consistent implementation for chain and chain.from_iterable
• General cleanup and typing
• Defined ownership rules
• Unittests

[codecov]

Codecov Report

Patch coverage: 90.69% and project coverage change: -0.19 ⚠️

Comparison is base (d20a48b) 99.25% compared to head (ad8c89c) 99.07%.

❗ Current head ad8c89c differs from pull request most recent head 872c26d. Consider uploading reports for the commit 872c26d to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
- Coverage   99.25%   99.07%   -0.19%     
==========================================
  Files          20       20              
  Lines        2017     2047      +30     
  Branches      308      314       +6     
==========================================
+ Hits         2002     2028      +26     
- Misses         10       11       +1     
- Partials        5        8       +3     

Impacted Files	Coverage Δ
unittests/test_itertools.py	98.01% <88.46%> (-1.99%)	⬇️
asyncstdlib/itertools.py	98.62% <94.11%> (-0.45%)	⬇️

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