huge speed optimization on HDD by removing md5 (#845)

* Eliminate unnecessary use of MD5 checksum

md5checksum() computes the actual checksum of a specified file, which is appropriately expensive, but the code seemed to be using the checksum result as a key into the imgMetadata dictionary to avoid handling image files being renamed during processing steps. This seems like a very expensive way to handle the rename so instead, I now update the imgMetadata keys with the new filename in the one place that the rename happens, and avoid MD5 checksums entirely.

* merge conflicts

* Add missing handling for image path renames due to nested chapter folder name

* merge conflicts

* merge conflicts

* add perf_counters

* imgFileProcessing perf_counter

* use startswith and removeprefix

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Co-authored-by: utopiafallen <utopiafallen@gmail.com>

kindlecomicconverter/shared.py

@@ -75,16 +75,6 @@ def walkLevel(some_dir, level=1):
             del dirs[:]
 
 
-def md5Checksum(fpath):
-    with open(fpath, 'rb') as fh:
-        m = md5()
-        while True:
-            data = fh.read(8192)
-            if not data:
-                break
-            m.update(data)
-        return m.hexdigest()
-
 
 def sanitizeTrace(traceback):
     return ''.join(format_tb(traceback))\