fix(db): ensure type is str before trying to deserialize

[whitdog47]

This pull request addresses a potential issue in the search_filter_sort_paginate function within the database service by ensuring that the filter_spec is of type str before attempting to deserialize it using json.loads.

Key Changes

• Type Check for Deserialization:
  • Added a type check to ensure filter_spec is a string before calling json.loads.
  • This prevents errors that could occur if filter_spec is not a string, enhancing the robustness of the deserialization process.

Files Changed

• src/dispatch/database/service.py:
  • Modified the search_filter_sort_paginate function to include a type check for filter_spec.
  • Modified the type signature for filter_spec to reflect that it can be None, str, or a dict.
  • Added a comment to help future developers understand why the type check was added.