feat: Propagate results and errors to task awaiters in ptaskgroup

[achimnol]

• This allows the caller can await and handle exceptions in the task if they want to, beside the persistent task group's owne exception handler.

[codecov[bot]]

Codecov Report

Merging #44 (d5ce553) into main (cc4ba30) will decrease coverage by 0.42%. The diff coverage is 48.57%.

:exclamation: Current head d5ce553 differs from pull request most recent head e737f4c. Consider uploading reports for the commit e737f4c to get more accurate results

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
- Coverage   65.96%   65.54%   -0.43%     
==========================================
  Files          16       16              
  Lines        1281     1306      +25     
==========================================
+ Hits          845      856      +11     
- Misses        436      450      +14     

Impacted Files	Coverage Δ
src/aiotools/taskgroup/persistent.py	0.00% <0.00%> (ø)
src/aiotools/taskgroup/persistent_compat.py	83.33% <94.44%> (+0.09%)	:arrow_up:

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