feat: fusiondb compatibility

This MR provides compatibility with fusiondb. It adds integration tests on changes proposed by external contributers and harmonizes the code style.

Existing application does not work with Fusion due to different implementation of collection function. Fusion does not return non-XML content such as XQuery files which means the endpoints are not found. There is also a function name clash in openapi-tests-simple.xqm which creates an error in Fusion with the sample endpoints.

Issue is resolved with recursive functions that use xmldb functions in order to find child resources and collections to build the list of uris in place of existing base-uri function. This works in both Fusion and eXist

There is also an extension to the list of recognised xquery file extensions to cover other used formats.