Disable PCodec if dependencies are unavailable

Author: jakirkham

numcodecs/__init__.py

@@ -144,6 +144,7 @@
 
 register_codec(Fletcher32)
 
-from numcodecs.pcodec import PCodec
+with suppress(ImportError):
+    from numcodecs.pcodec import PCodec
 
-register_codec(PCodec)
+    register_codec(PCodec)

numcodecs/pcodec.py

@@ -3,10 +3,7 @@
 from numcodecs.abc import Codec
 from numcodecs.compat import ensure_contiguous_ndarray
 
-try:
-    from pcodec import ChunkConfig, ModeSpec, PagingSpec, standalone
-except ImportError:  # pragma: no cover
-    standalone = None
+from pcodec import ChunkConfig, ModeSpec, PagingSpec, standalone
 
 
 DEFAULT_MAX_PAGE_N = 262144
@@ -49,9 +46,6 @@ def __init__(
         # TODO one day, add support for the Try* mode specs
         mode_spec: Literal['auto', 'classic'] = 'auto',
     ):
-        if standalone is None:  # pragma: no cover
-            raise ImportError("pcodec must be installed to use the PCodec codec.")
-
         # note that we use `level` instead of `compression_level` to
         # match other codecs
         self.level = level