fix: support PEP 639 SPDX license identifiers in pyproject.toml

[bigcat88]

Using the modern PEP 639 SPDX license format like license = "MIT" in pyproject.toml would trigger a spurious warning asking users to switch to the deprecated license = {file = "LICENSE"} format. The parser already handled string licenses correctly internally, it just warned about them unnecessarily.

Removed the warning for string license values since license = "MIT" is the current recommended format per PEP 639. Also updated comfy node init to generate license = "MIT" instead of license = {file = "LICENSE"} in new pyproject.toml files. The deprecated dict formats ({file = "..."} and {text = "..."}) continue to work without warnings.

Fixes #295

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #383      +/-   ##
==========================================
- Coverage   63.92%   63.89%   -0.03%     
==========================================
  Files          33       33              
  Lines        3703     3700       -3     
==========================================
- Hits         2367     2364       -3     
  Misses       1336     1336              

Files with missing lines	Coverage Δ
comfy_cli/registry/config_parser.py	93.42% <100.00%> (-0.13%)	⬇️

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