Fix XPC file handle ownership

[fallintoplace]

Summary

• Make file handles returned by XPCMessage own their duplicated descriptors.
• Keep caller-owned FileHandle values open when adding them to an XPC message.
• Close the unused log descriptor in the container and machine log commands.
• Add repeated log/dial descriptor lifetime tests.

xpc_fd_create duplicates its input descriptor, so the setters do not need to consume the caller's FileHandle. The getters also duplicate descriptors; making the returned handles close on deallocation gives those descriptors a clear owner and prevents repeated log/dial operations from leaking them.

Validation

• DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer make test
• Swift format lint
• Hawkeye license check