Provide a type and memory safe interface for `attribute`

This feature request is a continuation of this thread https://github.com/AcademySoftwareFoundation/OpenImageIO/pull/4560 aiming to provide a more type safe interface for setting and reading attributes rather than reading from a raw pointer.

This would be done as an addendum to the current API with the other calls then slowly being deprecated over time
```[tasklist]
### Tasks
- [ ] Create `attribute` function taking a cspan
- [ ] Update all the related `getattribute` etc. functions to reflect these changes
```

Start by reading the linked pull request and the current attribute, getattribute, and related API declarations and implementations. The issue names no files or tests. Done means adding the cspan-based attribute interface, updating the related functions, and identifying the existing calls for gradual deprecation.

Written by the indexing model from the issue text.