Allow `tensorflow-text[cpu]`

[t-kalinowski]

Currently, pulling in tensorflow-text pulls in a requirement for tensorflow. However, if a project already has tensorflow-cpu declared, then it leads to both tensorflow and tensorflow-cpu being installed in the virtual environment.

It would be ideal if it was possible to install a CPU-only version of tensorflow-text.

This comes up in contexts like:

astral-sh/uv#4422 (comment)