Enable ruff/flake8-implicit-str-concat rules (ISC) and fix issues

[DimitriPapadopoulos]

Note: #1868 is the same applied to the v3 branch

    ISC001 Implicitly concatenated string literals on one line
    ISC003 Explicitly concatenated string should be implicitly concatenated

This rule is currently disabled because it conflicts with the formatter: https://github.com/astral-sh/ruff/issues/8272

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
• [x] Changes documented in docs/release.rst
• [x] 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 99.98%. Comparing base (cb4230d) to head (cc10491). Report is 24 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##           main    #1837       +/-   ##
=========================================
+ Coverage      0   99.98%   +99.98%     
=========================================
  Files         0       38       +38     
  Lines         0    14667    +14667     
=========================================
+ Hits          0    14665    +14665     
- Misses        0        2        +2     

Files with missing lines	Coverage Δ
zarr/_storage/store.py	100.00% <100.00%> (ø)
zarr/indexing.py	100.00% <100.00%> (ø)

... and 36 files with indirect coverage changes

[jhamman]

@DimitriPapadopoulos - thanks for moving your focus over to the v3 branch. I'm going to close this in favor of the contributions you've already made there. 🙏