Increase test coverage for @data-eden/network

[rwjblue]

• add tests for a middleware to handle errors in following middlewares (and "recovering")
• add cases where HTTP method is changed by the middleware (aka "query tunneling")
• calling buildFetch([]) (e.g. when you don't have any middlewares)
• calling buildFetch with a few different middlewares that rely on ordering, and assert that they are called in the correct order
• calling buildFetch multiple times makes the first call throw a custom error