feat: Removed Column Index lookup

[bbernays]

Summary

Simplified implementation of #2592 that handles the main call site. In the future we can look at implementing a more fully implemented cache

[erezrokah]

My suggestion in #2592 was wrong. TransformWithStruct defaults every column to schema.PathResolver, which calls r.Set(c.Name, ...), so the Resolver == nil branch here is almost never taken and the linear lookup stays.

To cover it, make Set itself fast: store the current column index on the resource before calling the resolver, and have Set check it first.

// schema/resource.go
type Resource struct {
    // ...
    columnIndexHint int
}

func (r *Resource) Set(columnName string, value any) error {
    index := r.columnIndexHint
    if index < 0 || index >= len(r.data) || r.Table.Columns[index].Name != columnName {
        index = r.Table.Columns.Index(columnName)
        if index == -1 {
            panic(columnName + " column not found")
        }
    }
    // existing r.data[index].Set(value) + panic on error
}

func (r *Resource) setColumnIndexHint(i int) { r.columnIndexHint = i }

resolveColumn calls resource.setColumnIndexHint(colIndex) before column.Resolver(...) or Set. Since scheduler/resolvers is a separate package, the setter must be exported (or the loop moves into schema). This removes the need for SetWithIndex.