Fix exception when rebuilding graph for tasks with static sub-namespace of dynamic namespace

[ahkole]

This closes #183.

From my debugging, I think the issue is caused by the assumption in links_from_dict that the leaf socket in the socket_path is in a dynamic namespace, which is not always the case (see minimal example in the issue, which I also added as an additional test). This leads to an exception when it tries to assert that the parent of the leaf socket is a dynamic namespace. To fix this, we now first check if the leaf socket is not already in the parent namespace before trying to add it as a dynamic child. If the leaf socket is already present, we simply use it as the target.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.76%. Comparing base (8d85e61) to head (cb88da7).

Files with missing lines	Patch %	Lines
src/node_graph/graph.py	62.50%	3 Missing ⚠️
tests/test_graph.py	88.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #184      +/-   ##
==========================================
+ Coverage   89.68%   89.76%   +0.08%     
==========================================
  Files          81       81              
  Lines        8984     9001      +17     
==========================================
+ Hits         8057     8080      +23     
+ Misses        927      921       -6     

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