Optimize FieldVector conversion to avoid unnecessary container cloning

[anim001k]

Summary

Replace full container cloning with element-wise iteration in FieldVector<T> to FieldVector<U> conversion.

Problem

The From<&'a FieldVector<T>> for FieldVector<U> implementation was performing unnecessary full container cloning:

FieldVector(other.clone().into_iter().map(Into::into).collect())

This creates an intermediate Vec<T> allocation before converting elements, causing:

• Unnecessary memory allocation and copying
• Temporary memory pressure (doubling memory usage)
• Performance degradation on large vectors

Solution

Replace with direct iteration over references with element cloning:

FieldVector(other.0.iter().cloned().map(Into::into).collect())