Migrate numpy namespace to numpy 2.0

[grasskin]

Numpy 2.0 deprecates part of their namespace, see https://numpy.org/doc/stable/numpy_2_0_migration_guide.html for all details.
Keras is affected by np.Inf -> np.inf and np.unicode_ -> np.str_.

[hertschuh]

Thanks!

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.27%. Comparing base (7d92e9e) to head (b28f425).

Files	Patch %	Lines
keras/src/callbacks/reduce_lr_on_plateau.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #20049   +/-   ##
=======================================
  Coverage   79.27%   79.27%           
=======================================
  Files         501      501           
  Lines       46921    46921           
  Branches     8648     8648           
=======================================
  Hits        37195    37195           
  Misses       7981     7981           
  Partials     1745     1745           

Flag	Coverage Δ
keras	79.12% <83.33%> (ø)
keras-jax	62.46% <83.33%> (ø)
keras-numpy	57.51% <0.00%> (ø)
keras-tensorflow	63.80% <83.33%> (ø)
keras-torch	62.51% <83.33%> (ø)

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[fchollet]

LGTM, thanks for the fix!

[adamjstewart]

Probably closes #19691