Rethinking Zarr's core dependencies

[jhamman]

I'd like to open the conversation about what Zarr's core dependencies are for 3.0. Currently, this looks like:

zarr-python/pyproject.toml

Lines 25 to 34 in 1131253

	dependencies = [
	'asciitree',
	'numpy>=1.25',
	'fasteners',
	'numcodecs>=0.10.2',
	'fsspec>2024',
	'crc32c',
	'typing_extensions',
	'donfig',
	]

Some of these are not used anymore (asciitree and fasteners) so those can safely go.

Then there is fsspec and crc32c. These are only needed for the RemoteStore and ShardingCodec, respectively. What do we think about making these optional?

One proposed diff in our dependencies would look something like:

 dependencies = [
-    'asciitree',
     'numpy>=1.25',
-    'fasteners',
-    'numcodecs>=0.10.2',
-    'fsspec>2024',
-    'crc32c',
+    'numcodecs>=0.12',
     'typing_extensions',
     'donfig',
 ]

 [project.optional-dependencies]
+remote = [
+    "fsspec",
+]
+sharding = [
+    "crc32c",
+]

Notes:

• fsspec is pure python with no dependencies so is not a particular heavy dependency.
• crc32c could potentially move into numcodecs, right?