fix: accept uint8 dtype aliases in Zarr v2

[guhou-hvi]

Summary

Addresses #3622.

A single-byte element has no internal byte ordering, so <u1, >u1 and
|u1 can describe the same uint8 data. Currently only |u1 is registered
as a UInt8 v2 name: the stored bytes are valid, but metadata parsing rejects
the two aliases and prevents the array from opening.

This accepts both aliases while keeping |u1 as the serialized name.

For reviewers

The implementation extends only the accepted UInt8 v2 names. <u1 and >u1
are accepted on input, while serialization remains |u1. Tests cover dtype
and registry parsing, reading local arrays containing [0, 128, 255],
canonical serialization, unchanged on-disk metadata after read-only access,
and rejection of invalid names and object codecs. Other dtypes and v3 are unchanged.

Local validation run by Codex on Windows with Python 3.12.2:

• Selected dtype, registry, v2 metadata and array modules: 2978 passed, 758 skipped.
• Ruff, formatting, spelling, docstring checks and changelog draft build passed.
• Native Windows mypy reports two existing unused-ignore errors in
  tests/test_store/test_local.py, reproduced on main in the same environment.
  mypy --platform linux passes for 196 files; this is type analysis, not a Linux runtime test.

Codex implemented the code, tests and changelog, ran the local checks, and
translated and polished my explanation, and prepared the validation notes. A separate Codex agent performed a static review.
I have reviewed and understand the changes.

Author attestation

• I am a human, these are my changes, and I have reviewed and understood every change and can explain why each is correct.

TODO

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions — no new API
• New/modified features documented in docs/user-guide/*.md — bug fix; changelog added
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.22%. Comparing base (ae41d6e) to head (a2787b6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4381   +/-   ##
=======================================
  Coverage   94.22%   94.22%           
=======================================
  Files          92       92           
  Lines       12942    12942           
=======================================
  Hits        12195    12195           
  Misses        747      747           

Files with missing lines	Coverage Δ
src/zarr/core/dtype/npy/int.py	99.38% <100.00%> (ø)

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