feat: load packet logs from configured source

internal/isphere/file_source_test.go

@@ -0,0 +1,29 @@
+package isphere
+
+import (
+	"os"
+	"reflect"
+	"testing"
+)
+
+func TestLoadEncryptedPacketLogSourceFromFileReadsNonEmptyLines(t *testing.T) {
+	path := writePacketLogFileForTest(t, "\n  encrypted-line-1  \r\n\r\n\tencrypted-line-2\n")
+
+	got, err := LoadEncryptedPacketLogSourceFromFile(path)
+	if err != nil {
+		t.Fatalf("LoadEncryptedPacketLogSourceFromFile returned error: %v", err)
+	}
+	want := EncryptedPacketLogSource{Lines: []string{"encrypted-line-1", "encrypted-line-2"}}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("source = %#v, want %#v", got, want)
+	}
+}
+
+func writePacketLogFileForTest(t *testing.T, content string) string {
+	t.Helper()
+	path := t.TempDir() + "\\packet.log"
+	if err := os.WriteFile(path, []byte(content), 0o600); err != nil {
+		t.Fatalf("write test packet log: %v", err)
+	}
+	return path
+}