Add typing to Array.__init__

[dstansby]

Adds typing to the signature of Array.__init__.

TODO:

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.99%. Comparing base (6fe553d) to head (f5b89de).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1710   +/-   ##
=======================================
  Coverage   99.99%   99.99%           
=======================================
  Files          38       38           
  Lines       14580    14583    +3     
=======================================
+ Hits        14579    14582    +3     
  Misses          1        1           

Files	Coverage Δ
zarr/core.py	100.00% <100.00%> (ø)