chore: slightly optimise rename detection (ref #10777) (#10819)

Only run rename detection for new files. This skips an expensive check
for all updates to existing files. The tradeoff is that we no longer
immediately detect renames on top of another file as a rename -- this
may instead become a copy+delete operation on the destination.

---------

Signed-off-by: Jakob Borg <jakob@kastelo.net>

lib/protocol/bep_fileinfo.go

@@ -146,6 +146,8 @@ type FileInfo struct {
 	Deleted       bool
 	NoPermissions bool
 
+	New bool // set by the scanner when the file newly appeared on disk; no db / wire representation
+
 	truncated bool // was created from a truncated file info without blocks
 }
 
@@ -233,7 +235,8 @@ func (f *FileInfo) LogAttr() slog.Attr {
 	case FileInfoTypeFile:
 		kind = "file"
 		if !f.Deleted {
-			attrs = append(attrs,
+			attrs = append(
+				attrs,
 				slog.Any("modified", f.ModTime()),
 				slog.String("permissions", fmt.Sprintf("0%03o", f.Permissions)),
 				slog.Int64("size", f.Size),