Added support for nested JAR paths

[wduncanfraser]

As of Spring 3.2, the default loader has moved form standard "jar" paths to "nested". This is meant to be a drop in replacement for standard Jar path loading.

https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.2-Release-Notes#nested-jar-support

https://javadoc.io/doc/org.springframework.boot/spring-boot-loader/latest/org/springframework/boot/loader/net/protocol/nested/package-summary.html

Without this change, using >= Spring 3.2.x would result in an exception like:

Caused by: net.pwall.json.schema.JSONSchemaException: Error reading schema file - nested:/app/some-service.jar/!BOOT-INF/classes/!/library/some-schema.yaml

Simply adds nested as a supported scheme, leveraging the existing jar support.