Add Esplora blockchain backend support

        This commit adds support for using Esplora as a blockchain backend for LND,
        enabling operation without requiring a full Bitcoin node (btcd/bitcoind).

        Key features:
        - Esplora chain client implementation for block/transaction queries
        - Esplora chain notifier for confirmations and spend notifications
        - Esplora fee estimator with smart fee selection
        - FilteredChainView implementation for routing
        - Gap limit scanning for wallet recovery
        - Optimized block scanning with progress logging

        Configuration:
        - bitcoin.node=esplora
        - esplora.url=<esplora-api-url>
        - esplora.requesttimeout=30s
        - esplora.maxretries=3
        - esplora.pollinterval=10s

        Co-Authored-By: Nitesh Balusu <niteshbalusu@icloud.com>

Author: kaloudis

chainntnfs/esploranotify/driver.go

@@ -0,0 +1,60 @@
+package esploranotify
+
+import (
+	"fmt"
+
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/lightningnetwork/lnd/blockcache"
+	"github.com/lightningnetwork/lnd/chainntnfs"
+	"github.com/lightningnetwork/lnd/esplora"
+)
+
+// createNewNotifier creates a new instance of the EsploraNotifier from a
+// config.
+func createNewNotifier(args ...interface{}) (chainntnfs.ChainNotifier, error) {
+	if len(args) != 5 {
+		return nil, fmt.Errorf("incorrect number of arguments to "+
+			"createNewNotifier, expected 5, got %d", len(args))
+	}
+
+	client, ok := args[0].(*esplora.Client)
+	if !ok {
+		return nil, fmt.Errorf("first argument must be an " +
+			"*esplora.Client")
+	}
+
+	chainParams, ok := args[1].(*chaincfg.Params)
+	if !ok {
+		return nil, fmt.Errorf("second argument must be a " +
+			"*chaincfg.Params")
+	}
+
+	spendHintCache, ok := args[2].(chainntnfs.SpendHintCache)
+	if !ok {
+		return nil, fmt.Errorf("third argument must be a " +
+			"chainntnfs.SpendHintCache")
+	}
+
+	confirmHintCache, ok := args[3].(chainntnfs.ConfirmHintCache)
+	if !ok {
+		return nil, fmt.Errorf("fourth argument must be a " +
+			"chainntnfs.ConfirmHintCache")
+	}
+
+	blockCache, ok := args[4].(*blockcache.BlockCache)
+	if !ok {
+		return nil, fmt.Errorf("fifth argument must be a " +
+			"*blockcache.BlockCache")
+	}
+
+	return New(client, chainParams, spendHintCache, confirmHintCache,
+		blockCache), nil
+}
+
+// init registers a driver for the EsploraNotifier.
+func init() {
+	chainntnfs.RegisterNotifier(&chainntnfs.NotifierDriver{
+		NotifierType: notifierType,
+		New:          createNewNotifier,
+	})
+}