Fix error variable scoping in generated code templates - #1

This PR fixes the issue with error variable reuse in generated API handlers by changing all error handling patterns to use scoped declarations.

Changes made:

• Removed global err variable declarations at function scope
• Converted all error checks to use scoped declarations (if err := ...)
• Updated error handling patterns in all major framework templates:
  • Chi
  • Echo
  • Fiber
  • Gorilla
  • StdHTTP

The changes cover all parameter types:

• Path parameters
• Query parameters
• Header parameters
• Cookie parameters
• JSON unmarshaling
• Parameter binding
• Styled parameter binding

This change prevents potential issues with error variable reuse and makes the generated code safer and more maintainable.

Created with Solver