Starting from Cython >=3.0.8, readonly fused typed memoryviews are finally allowed. Meaning we can add const qualifiers to memoryviews so that readonly arrays do not get rejected. We should audit our usage of memoryviews with fused dtypes and sprinkle const pretty much everywhere.
#20195 gives a representative example.

EDIT: a good way to go about this is one PR per submodule, using a grep like in #20196 (comment) to identify files to audit.

• _lib (no usage)
• cluster (ENH: array types: add JAX support #20085)
• fftpack (no usage)
• linalg (MAINT: linalg: add const to Cython function signatures #20837)
• integrate (no usage)
• interpolate (MAINT: interpolate: const qualify cython arrays #20250, MAINT: interpolate: add const to Cython function signatures #20872)
• io (no usage)
• ndimage (no usage)
• optimize (ENH: optimize: const qualify Cython array arguments #20265)
• signal (MAINT: signal: add const to Cython function signatures #20887)
• sparse (MAINT: sparse: add const to Cython function signatures #20873)
• spatial (MAINT: spatial: add const to Cython function signatures #20874)
• special (no usage)
• stats (MAINT: stats: add const to Cython function signatures #20891)