Test endianess support against zarr-python data types refactor

[TomNicholas]

This PR is for testing support for @d-v-b's unmerged zarr data types refactor in zarr-developers/zarr-python#2874. Particularly we care about supporting big-endian data.

• Closes #xxxx
• Tests added
• Tests passing
• Full type hint coverage
• Changes are documented in docs/releases.rst
• New functions/methods are listed in api.rst
• New functionality has documentation

[TomNicholas]

This is still using the wrong installed version 😞

We would appreciate you help with this @maxrjones

[ianhi]

hooray!

[maxrjones]

yeah the proper version is installed for the upstream tests (removing and adding test-upstream should trigger those) but looks like there'll be lots of failures and the tests are running slower - https://github.com/zarr-developers/VirtualiZarr/actions/runs/14409577052/job/40414132555?pr=545.

[maxrjones]

might be worth trying the upstream tests out locally because it looks like the CI's hanging

[d-v-b]

Suggested change

	'zarr @ git+https://github.com/ianhi/zarr-python@feat/fixed-length-strings',
	'zarr @ git+https://github.com/d-v-b/zarr-python@feat/fixed-length-strings',

[TomNicholas]

Now that zarr-developers/zarr-python#2874 was merged upstream our normal upstream tests should be able to run against the updated zarr-python.

However I messed this PR up by merging from main (instead of develop) when trying to update it and instead of wasting time trying to untangle my git mess I just made another PR (#618) to replace this one. 🙃