Introduce Comparable protocol

src/aligntools/cigar_hit.py

@@ -12,6 +12,7 @@
 from aligntools.coordinate_mapping import CoordinateMapping
 from aligntools.cigar_actions import CigarActions
 from aligntools.cigar import Cigar
+from aligntools.comparable import Comparable
 import aligntools.exceptions as ex
 
 
@@ -397,7 +398,7 @@ def __str__(self):
 
 
 def drop_overlapping_cigar_hits(cigar_hits: Iterable[CigarHit],
-                                quality: Callable[[CigarHit], int]) \
+                                quality: Callable[[CigarHit], Comparable]) \
         -> Iterator[CigarHit]:
     """
     Filter overlapping CigarHit objects based on a quality criterion.

src/aligntools/comparable.py

@@ -0,0 +1,13 @@
+from typing import Protocol, TypeVar, runtime_checkable
+
+T = TypeVar('T', bound='Comparable')
+
+
+@runtime_checkable
+class Comparable(Protocol):
+    def __lt__(self, other: T) -> bool: ...
+    def __le__(self, other: T) -> bool: ...
+    def __gt__(self, other: T) -> bool: ...
+    def __ge__(self, other: T) -> bool: ...
+    def __eq__(self, other: object) -> bool: ...
+    def __ne__(self, other: object) -> bool: ...