Cdk ldk node (#904)

* 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

---------

Co-authored-by: Erik <78821053+swedishfrenchpress@users.noreply.github.com>

misc/scripts/filtered_ldk_node_log.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+# Filtered log viewer for LDK Node that excludes "falling back to default fee rate" messages
+# Usage: ./misc/scripts/filtered_ldk_node_log.sh [log_file_path]
+
+LOG_FILE="$1"
+
+# If no log file specified, use the default pattern
+if [ -z "$LOG_FILE" ]; then
+    LOG_FILE="$CDK_ITESTS_DIR/ldk_mint/ldk_node.log"
+fi
+
+# Wait for log file to exist, then tail it with filtering
+while [ ! -f "$LOG_FILE" ]; do 
+    sleep 1
+done
+
+# Tail the log file and filter out fee rate fallback messages
+tail -f "$LOG_FILE" | grep -v -E "Falling back to default of 1 sat/vb|Failed to retrieve fee rate estimates"