Define all floats in interval methods to be float64 to match constructor

[ColtonPayne]

Summary

Fixes a type inconsistency where intersection methods used np.float32 for default values when intervals are disjoint, while the Interval struct fields are defined as float64. Changed all default float values to np.float64 to match the constructor and avoid type coercion issues.

Changes:

• interval.py: Updated disjoint-interval defaults from np.float32 to np.float64
• interval_type.py: Same fix in the overloaded intersection used by JIT-compiled code

Issues

Closes #87
Closes #88

[kmukherji]

Approved. Says merging is blocked.