Change default cast_policy to numpy+floatX to fix float downcasting

[ayulockedin]

Description

This PR changes the default cast_policy in configdefaults.py to numpy+floatX. This removes the older NumpyAutocaster machinery which was causing inconsistent float downcasting (e.g., downcasting 9.0 to float32 while keeping 8.9 and 9.1 as float64).

Opening this as a draft PR first to let the CI test suite evaluate the overall impact. Changing this core default will likely require updating type assertions across the broader test suite where the old downcasting behavior was explicitly expected.

Related Issue

• Closes Default casting to int8 leads to easy overflow errors #1073
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

[ayulockedin]

i have changed the default to see what the damage cuz i think all tests would also be relying on the old NumpyAutocaster here, lets see what the blast radius is