numpy 2.0 removal

[ericpre]

Use ruff check . --select NPY201 to find these.

For reference: https://numpy.org/devdocs/release/2.0.0-notes.html#numpy-2-0-python-api-removals.

Progress of the PR

• Replace deprecated np.string_ by np.bytes_,
• [n/a] update docstring (if appropriate),
• [n/a] update user guide (if appropriate),
• add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:rosettasciio build of this PR (link in github checks)
• [n/a] add tests,
• ready for review.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 86.36%. Comparing base (24fc42d) to head (fd8b1d5).

Files	Patch %	Lines
rsciio/utils/tools.py	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #238   +/-   ##
=======================================
  Coverage   86.36%   86.36%           
=======================================
  Files          83       83           
  Lines       10604    10604           
  Branches     2307     2307           
=======================================
  Hits         9158     9158           
  Misses        930      930           
  Partials      516      516           

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