Add zone task

[superstar54]

• fix the context manager
• Add If and While zone

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.46%. Comparing base (026e11a) to head (f6e7d2f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_graph/task.py	72.72%	15 Missing ⚠️
src/node_graph/tasks/builtins.py	68.18%	7 Missing ⚠️
src/node_graph/manager.py	91.83%	4 Missing ⚠️
tests/test_zone.py	94.23%	3 Missing ⚠️
src/node_graph/socket.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
- Coverage   90.47%   90.46%   -0.02%     
==========================================
  Files          78       79       +1     
  Lines        7825     7980     +155     
==========================================
+ Hits         7080     7219     +139     
- Misses        745      761      +16     

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