Enable ruff PTH (flake8-use-pathlib) and fix all findings

Replaces os.path/open()/os.stat()/os.chmod() calls with their Path
method equivalents across src, tests, misc, and bin, wrapping str
variables in Path(...) where they must stay str for other uses (e.g.
subprocess argv, CLI-arg formatting). helpers.safe_symlink() now
decodes StrOrBytesPath to a str Path via os.fsdecode() upfront, same
pattern already used elsewhere for the str|bytes union.

tests/plugins/tesseract_debug_rotate.py

@@ -74,11 +74,11 @@ class FixedRotateNoopOcrEngine(OcrEngine):
     def generate_hocr(input_file, output_hocr, output_text, options):
         with (
             Image.open(input_file) as im,
-            open(output_hocr, 'w', encoding='utf-8') as f,
+            output_hocr.open('w', encoding='utf-8') as f,
         ):
             w, h = im.size
             f.write(HOCR_TEMPLATE.format(str(w), str(h)))
-        with open(output_text, 'w') as f:
+        with output_text.open('w') as f:
             f.write('')
 
     @staticmethod

tests/plugins/tesseract_noop.py

@@ -72,11 +72,11 @@ class NoopOcrEngine(OcrEngine):
     def generate_hocr(input_file, output_hocr, output_text, options):
         with (
             Image.open(input_file) as im,
-            open(output_hocr, 'w', encoding='utf-8') as f,
+            output_hocr.open('w', encoding='utf-8') as f,
         ):
             w, h = im.size
             f.write(HOCR_TEMPLATE.format(str(w), str(h)))
-        with open(output_text, 'w') as f:
+        with output_text.open('w') as f:
             f.write('')
 
     @staticmethod