Single startswith() call instead of multiple ones

[DimitriPapadopoulos]

It's faster and probably more readable.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[jhamman]

Thanks @DimitriPapadopoulos.

(fyi, this code path will be leaving Zarr soon but no harm in merging for now)

[jakirkham]

Wonder if this is part of performance degradation with v3 that was called out before

cc @rabernat (for awareness)

[DimitriPapadopoulos]

Replacing two function calls with a single function call should be faster, unless key.startswith("data/") is usually true. In that case, the second function call key.startswith("meta/") would seldom be triggered. But this would actually happen only when a ValueError is raised, which shouldn't happen too often and is expensive in itself.