Improve compatibility with newer Java, Spring, and Windows file handling

[jlouvel]

• Improve compatibility with newer Java and Spring APIs across the Restlet modules touched locally.
• Make upload and zip temporary file creation work on non-POSIX file systems such as Windows by applying POSIX permissions only when supported.
• Tighten Spring bean resolution and null-safety handling in the Spring extension and its tests.
• Ensure zip entry/request streams are released more reliably and avoid duplicate media-type handling issues in core classes.
• Update integration points and tests for current library APIs and warnings in Gson, Jackson, FreeMarker, Jetty, JAAS, and related modules.