Remove the bytewise diffing of failed snapshots

In doing so this removes the file similarity value, and as such the key that
the failure report was sorted on. This was done because, given how many
snapshot tests we have now, if lots failed, it would take a long time (often
many minutes) to compile the report.

The report is now sorted on the test name.

Now, no matter how many snapshots fail, the report should be produced pretty
much instantly.

tests/snapshot_tests/conftest.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import difflib
 import os
 from dataclasses import dataclass
 from datetime import datetime
@@ -107,7 +106,6 @@ class SvgSnapshotDiff:
     snapshot: Optional[str]
     actual: Optional[str]
     test_name: str
-    file_similarity: float
     path: PathLike
     line_number: int
     app: App
@@ -132,17 +130,10 @@ def pytest_sessionfinish(
 
         if app:
             path, line_index, name = item.reportinfo()
-            similarity = (
-                100
-                * difflib.SequenceMatcher(
-                    a=str(snapshot_svg), b=str(actual_svg)
-                ).ratio()
-            )
             diffs.append(
                 SvgSnapshotDiff(
                     snapshot=str(snapshot_svg),
                     actual=str(actual_svg),
-                    file_similarity=similarity,
                     test_name=name,
                     path=path,
                     line_number=line_index + 1,
@@ -152,7 +143,7 @@ def pytest_sessionfinish(
             )
 
     if diffs:
-        diff_sort_key = attrgetter("file_similarity")
+        diff_sort_key = attrgetter("test_name")
         diffs = sorted(diffs, key=diff_sort_key)
 
         conftest_path = Path(__file__)