DEP: Deprecate numpy.fix in favor of numpy.trunc - #30644

Summary

Deprecate numpy.fix as it provides identical functionality to numpy.trunc but is slower and is not part of the Array API standard.

Motivation

As noted in #30096:

• numpy.fix and numpy.trunc produce identical results
• numpy.trunc is ~2.5x faster than numpy.fix
• The Array API standard defines trunc but not fix
• The name trunc is clearer and more standard

Changes

• Add DeprecationWarning to numpy.fix()
• Update docstring with .. deprecated:: directive
• Add tests to verify deprecation warning is emitted
• Update existing tests to suppress deprecation warnings during functional tests
• Add release note about deprecation

Performance comparison

In [1]: arr = np.random.random(1_000_000)*1000

In [2]: %timeit np.trunc(arr)
426 μs ± 15.1 μs per loop

In [3]: %timeit np.fix(arr)
1.06 ms ± 3.34 μs per loop

In [4]: np.all(np.trunc(arr) == np.fix(arr))
Out[4]: np.True_

Closes #30096