Refactor position_in_template to look at template property directly

Don’t need the wrapper method on the `EmailPreviewTemplate` object now
that placeholders are an `InsensitiveSet` so we can do
`placeholders.index` directly

Author: quis

app/models/template_email_file.py

@@ -1,5 +1,7 @@
+import math
 import mimetypes
 import uuid
+from contextlib import suppress
 from datetime import UTC, datetime, timedelta
 from typing import Any
 
@@ -112,7 +114,9 @@ def file_contents(self):
 
     @property
     def position_in_template(self):
-        return self.template.index_of_placeholder(self.filename)
+        with suppress(KeyError):
+            return self.template.all_placeholders.index(self.filename)
+        return math.inf
 
 
 class TemplateEmailFiles(SerialisedModelCollection):

app/utils/templates.py

@@ -1,6 +1,4 @@
 import json
-import math
-from contextlib import suppress
 from typing import Any
 
 from flask import current_app, render_template, url_for
@@ -315,11 +313,6 @@ def all_placeholders(self):
     def placeholders(self):
         return OrderedSet([placeholder for placeholder in self.all_placeholders if placeholder not in self.filenames])
 
-    def index_of_placeholder(self, placeholder):
-        with suppress(KeyError):
-            return self.all_placeholders.index(placeholder)
-        return math.inf
-
 
 class LetterAttachment(JSONModel):
     id: Any