limit stagehand dep version to 0.5.9 due breaking changes

[thiagomoretto]

• The latest version (3.x) of the stagehand lib has breaking changes, so we have to limit the actual version to 0.5.9.
• Fixed the generate spec script that was failing to extract pydantic fields with default factory.
• Fixed the location of the generated file.
• Regenerated spec file, since the CI auto-gen is failing.