fix: resolve CI linting failures

- Removed unused imports (pathlib.Path, Schema, EnvVar, Optional)
- Fixed f-strings without placeholders in generator.py and validators.py
- Removed unused variables in generator.py
- Updated CI workflow to use correct project name (envschema)

envschema/formatters.py

@@ -1,7 +1,6 @@
 """Output formatters for validation results."""
 
 import json
-from typing import Optional
 
 from envschema.core import ValidationResult