* feat: add LDK Node Lightning backend with comprehensive integration
- Add new cdk-ldk-node crate implementing Lightning backend using LDK Node
- Extend MintPayment trait with start/stop methods for processor lifecycle management
- Add LDK Node configuration support to cdk-mintd with chain source and gossip options
- Enhance mint startup/shutdown to properly manage payment processor lifecycle
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Co-authored-by: Erik <78821053+swedishfrenchpress@users.noreply.github.com>
