Make IntoArrayVariant chain more explicit

[a10y]

Currently we implement IntoArrayVariant for all T: IntoCanonical by first calling into_canonical and then downcasting. This hides that there is a potentially expensive decoding step going on.

We should either remove the shortcut method, or rename the methods to make it clearer that they can be expensive

[robert3005]

Strong preference for single methods to avoid long chains. Need a good name though and likely will deviate from rust conventions

[a10y]

some options:

• canonicalize_to_primitive
• into_canonical_primitive
• to_canonical_primitive
• to_primitive

Another option is to replace methods with top-level function calls, e.g. canonical::to_primitive(array)

[robert3005]

I think into/to_canonical_primitive is likely what I would go for. Top level functions would also make it more explicit. Would try the rename and otherwise make them separate functions