Remove obsolete response objects from Fastly configuration

[cwillisf]

Resolves:

Supports POD-277

Changes:

Primary change: remove obsolete response objects from Fastly configuration before attempting to update or add any. This helps avoid exceeding the ~100-count limit.

Supporting changes:

• Type annotations, especially in fastly-extended.js, so I could tell what I was doing.
• Converted fastly-extended.js into a class so that the type annotations would work.
• Use Error instances for error reporting in configure-fastly.js, as opposed to using string.
  • Using string was incorrect as it violates the async library's expectations
  • It was also inconsistent: when reporting an error to the async library, we were sometimes passing a string and sometimes passing the output of the fastly library's request call, which uses Error.
• Reduced log output during redirect preprocessing

Test Coverage:

Existing tests updated

[Copilot]

Pull Request Overview

This PR refactors the Fastly configuration code to use proper type annotations and class-based structure, with the primary goal of removing obsolete response objects to avoid Fastly's count limits.

• Converted fastly-extended.js from function-based to class-based implementation to support type annotations
• Added proper error handling using Error instances instead of strings for consistency with async library expectations
• Enhanced Fastly configuration to clean up obsolete response objects before updates

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}