Improve pydantic model and dataclass usage

[superstar54]

Previously, Pydantic Models or dataclasses are annotation-only. But this is counterintuitive!

In this PR allows users to use pydantic model as inputs, and outputs direclty. No need to provide plain dict.

[codecov]

Codecov Report

❌ Patch coverage is 88.65979% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.18%. Comparing base (92a41de) to head (27906fd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_graph/utils/struct_utils.py	83.52%	14 Missing ⚠️
src/node_graph/socket_spec.py	53.84%	6 Missing ⚠️
src/node_graph/socket.py	80.00%	1 Missing ⚠️
tests/test_graph_task.py	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #142      +/-   ##
==========================================
+ Coverage   90.16%   90.18%   +0.01%     
==========================================
  Files          79       81       +2     
  Lines        8430     8617     +187     
==========================================
+ Hits         7601     7771     +170     
- Misses        829      846      +17     

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