Make default hash lib configurable without code changes via CLI argument (#3947)

* cli_args: Add --duplicate-check-hash-function.

* server.py: compare_image_hash configurable hash function

Uses an argument added in cli_args to specify the type of hashing to default to for duplicate hash checking.  Uses an `eval()` to identify the specific hashlib class to utilize, but ultimately safely operates because we have specific options and only those options/choices in the arg parser.  So we don't have any unsafe input there.

* Add hasher() to node_helpers

* hashlib selection moved to node_helpers

* default-hashing-function instead of dupe checking hasher

This makes a default-hashing-function option instead of previous selected option.

* Use args.default_hashing_function

* Use safer handling for node_helpers.hasher()

Uses a safer handling method than `eval` to evaluate default hashing function.

* Stray parentheses are evil.

* Indentation fix.

Somehow when I hit save I didn't notice I missed a space to make indentation work proper.  Oops!

server.py

@@ -25,6 +25,7 @@ import mimetypes
 from comfy.cli_args import args
 import comfy.utils
 import comfy.model_management
+import node_helpers
 from app.frontend_management import FrontendManager
 from app.user_manager import UserManager
 
@@ -161,10 +162,12 @@ class PromptServer():
             return type_dir, dir_type
 
         def compare_image_hash(filepath, image):
+            hasher = node_helpers.hasher()
+            
             # function to compare hashes of two images to see if it already exists, fix to #3465
             if os.path.exists(filepath):
-                a = hashlib.sha256()
-                b = hashlib.sha256()
+                a = hasher()
+                b = hasher()
                 with open(filepath, "rb") as f:
                     a.update(f.read())
                     b.update(image.file.read())