Add digest_directory parameter new_photo_ratelimit.

Initially inspired by the nuisance of having multiple photos
with the same timestamp because the system is too fast, this
feature could also be used to lessen disk load for running in
the background.

etiquette/photodb.py

@@ -20,6 +20,7 @@ from . import tag_export
 from voussoirkit import cacheclass
 from voussoirkit import expressionmatch
 from voussoirkit import pathclass
+from voussoirkit import ratelimiter
 from voussoirkit import spinal
 from voussoirkit import sqlhelpers
 
@@ -1192,6 +1193,7 @@ class PhotoDB(
             exclude_filenames=None,
             make_albums=True,
             new_photo_kwargs={},
+            new_photo_ratelimit=None,
             recurse=True,
             commit=True,
         ):
@@ -1208,6 +1210,8 @@ class PhotoDB(
                     photo = self.get_photo_by_path(filepath)
                 except exceptions.NoSuchPhoto:
                     photo = self.new_photo(filepath.absolute_path, commit=False, **new_photo_kwargs)
+                    if new_photo_ratelimit is not None:
+                        new_photo_ratelimit.limit()
 
                 photos.append(photo)
             return photos
@@ -1242,6 +1246,9 @@ class PhotoDB(
         if exclude_filenames is None:
             exclude_filenames = self.config['digest_exclude_files']
 
+        if isinstance(new_photo_ratelimit, (int, float)):
+            new_photo_ratelimit = ratelimiter.Ratelimiter(allowance=1, period=new_photo_ratelimit)
+
         if 'commit' in new_photo_kwargs:
             new_photo_kwargs.pop('commit')
         if 'filepath' in new_photo_kwargs: