Extract fetch utilities to a separate package

[cristinecula]

Problem

The fetch utilities in src/util/fetch/ duplicate functionality that exists in other Neovici packages (e.g., @neovici/core).

Current State

• cosmoz-queue has its own fetch wrapper with setBaseInit, fetch, json, jsonPost, etc.
• Similar utilities exist in other packages

Proposed Solution

Create a new public package (e.g., @neovici/fetch) containing:

• setBaseInit with getHeaders callback support
• fetch wrapper with header merging
• handleJSON, json, jsonPost, jsonPut, jsonPatch, jsonDelete
• RequestError class
• URL utilities

Benefits

• Single source of truth for fetch utilities
• Reusable across all Neovici packages
• Easier maintenance and consistent behavior