Cleanup crc32c soft dependency

Author: jakirkham

numcodecs/__init__.py

@@ -117,13 +117,17 @@
 
     register_codec(MsgPack)
 
-from numcodecs.checksum32 import CRC32, CRC32C, Adler32, JenkinsLookup3
+from numcodecs.checksum32 import CRC32, Adler32, JenkinsLookup3
 
 register_codec(CRC32)
-register_codec(CRC32C)
 register_codec(Adler32)
 register_codec(JenkinsLookup3)
 
+with suppress(ImportError):
+    from numcodecs.checksum32 import CRC32C
+
+    register_codec(CRC32C)
+
 from numcodecs.json import JSON
 
 register_codec(JSON)

numcodecs/checksum32.py

@@ -1,6 +1,7 @@
 import struct
 import zlib
 from collections.abc import Callable
+from contextlib import suppress
 from typing import TYPE_CHECKING, Literal
 
 import numpy as np
@@ -76,26 +77,25 @@ class CRC32(Checksum32):
     location = 'start'
 
 
-class CRC32C(Checksum32):
-    """Codec add a crc32c checksum to the buffer.
+_crc32c: Optional[ModuleType] = None
+with suppress(ImportError):
+    import crc32c as _crc32c
 
-    Parameters
-    ----------
-    location : 'start' or 'end'
-        Where to place the checksum in the buffer.
-    """
 
-    codec_id = 'crc32c'
+if _crc32c:
+    class CRC32C(Checksum32):
+        """Codec add a crc32c checksum to the buffer.
 
-    def checksum(self, buf):
-        try:
-            from crc32c import crc32c as crc32c_
+        Parameters
+        ----------
+        location : 'start' or 'end'
+            Where to place the checksum in the buffer.
+        """
 
-            return crc32c_(buf)
-        except ImportError:  # pragma: no cover
-            raise ImportError("crc32c must be installed to use the CRC32C checksum codec.")
+        codec_id = 'crc32c'
 
-    location = 'end'
+        checksum = _crc32c.crc32c
+        location = 'end'
 
 
 class Adler32(Checksum32):