Function navigate_pointer 

pub fn navigate_pointer<'a>(
    schema: &'a SchemaValue,
    root: &'a SchemaValue,
    pointer: &str,
) -> Result<&'a SchemaValue, String>

Walk a JSON Pointer path through a schema, resolving $ref at each step.

Segments are decoded per RFC 6901 (~1 → /, ~0 → ~). Returns the sub-SchemaValue at the given pointer, or an error.

Errors

Returns an error if a segment in the pointer cannot be resolved.