Changes

• Handle xml:base attribute on content (thanks @gleroi !)
• Replace lazy_static with OnceLock (thanks @rillian !)
• Support sub-categories from iTunes NS (thanks for the bug report @sophiawisdom !)
• Updates dependencies and MSRV to 1.77.2
• Pluggable ID generation (thanks for the bug report, patch and patience @nabijaczleweli ... will fix it properly next release)