fix: Minor cleanups and fixes

- Update NullJob to subclass Job
- Remove unnecessary size pre-read in _getMatches() as file sizes are
  already loaded during file scan via stat call
- Skip ref check if contents scan as the scan already prevents this from
  happening, some of the other scans do things differently and need to
  be reviewed before removing this post step completely
- Add guard on partial hashing to just hash the whole file if smaller
  than the offset and size and use the value for both the partial digest
  and digest

hscommon/jobprogress/job.py

@@ -7,7 +7,7 @@
 # http://www.gnu.org/licenses/gpl-3.0.html
 
 
-from typing import Any, Callable, Generator, Iterator, List, Union
+from typing import Any, Callable, Generator, List, Union
 
 
 class JobCancelled(Exception):
@@ -148,7 +148,7 @@ class Job:
         self._do_update(desc)
 
 
-class NullJob:
+class NullJob(Job):
     def __init__(self, *args, **kwargs) -> None:
         # Null job does nothing
         pass
@@ -161,9 +161,6 @@ class NullJob:
         # Null job does nothing
         pass
 
-    def iter_with_progress(self, sequence, *args, **kwargs) -> Iterator:
-        return iter(sequence)
-
     def start_job(self, *args, **kwargs) -> None:
         # Null job does nothing
         pass