Add spider functionality for relay crawling, marker management, and new SpiderMode config.

- Introduced the `spider` package for relay crawling, including periodic tasks and one-time sync capabilities.
- Added `SetMarker`, `GetMarker`, `HasMarker`, and `DeleteMarker` methods in the database for marker management.
- Updated configuration with `SpiderMode` and `SpiderFrequency` options to enable and customize spider behavior.
- Integrated `spider` initialization into the main application flow.
- Improved tag handling, NIP-70 compliance, and protected tag validation in event processing.
- Removed unnecessary logging and replaced `errorf` with `fmt.Errorf` for better error handling.
- Incremented version to `v0.5.0`.

pkg/database/markers.go

@@ -0,0 +1,62 @@
+package database
+
+import (
+	"github.com/dgraph-io/badger/v4"
+	"lol.mleku.dev/chk"
+)
+
+const (
+	markerPrefix = "MARKER:"
+)
+
+// SetMarker stores an arbitrary marker in the database
+func (d *D) SetMarker(key string, value []byte) (err error) {
+	markerKey := []byte(markerPrefix + key)
+	
+	err = d.Update(func(txn *badger.Txn) error {
+		return txn.Set(markerKey, value)
+	})
+	
+	return
+}
+
+// GetMarker retrieves an arbitrary marker from the database
+func (d *D) GetMarker(key string) (value []byte, err error) {
+	markerKey := []byte(markerPrefix + key)
+	
+	err = d.View(func(txn *badger.Txn) error {
+		item, err := txn.Get(markerKey)
+		if err != nil {
+			return err
+		}
+		
+		value, err = item.ValueCopy(nil)
+		return err
+	})
+	
+	return
+}
+
+// HasMarker checks if a marker exists in the database
+func (d *D) HasMarker(key string) (exists bool) {
+	markerKey := []byte(markerPrefix + key)
+	
+	err := d.View(func(txn *badger.Txn) error {
+		_, err := txn.Get(markerKey)
+		return err
+	})
+	
+	exists = !chk.E(err)
+	return
+}
+
+// DeleteMarker removes a marker from the database
+func (d *D) DeleteMarker(key string) (err error) {
+	markerKey := []byte(markerPrefix + key)
+	
+	err = d.Update(func(txn *badger.Txn) error {
+		return txn.Delete(markerKey)
+	})
+	
+	return
+}