Restore ability to store and query non-ASCII dataframe attributes

[johnkerl]

Up to and including the most recent 0.1.10 release of this package, we have supported the ability to store and query non-ASCII dataframe attributes.

As of the upcoming 0.1.11 release, this ability will be temporarily removed.

This accommodates #273 and TileDB-Inc/TileDB-Py#1304.

Context: this is a copy-reduction effort, removing the in-package conversion as discussed in detail in #99 from this package. In an upcoming TileDB Core release (perhaps early 2023) the ability to handle non-ASCII attributes will be restored, but the functionality will be in core. At that point in time we will have full Unicode ability, without in-package ASCII-to-Unicode conversion.

This issue remains open to track that core work, and to surface the temporary reduction in functionality for package users.

[johnkerl]

Dup of #415