Provide a caching option for OpenPGP UIF validity

[farblos]

One of these other-smartcard-features, described, for example, here:

For git rebases it would be helpful if the validity of a UIF touch event for the OpenPGP smartcard would be valid for at least a few seconds, so that not every single commit needed confirmation.

[robin-nitrokey]

See also: Nitrokey/opcard-rs#106

[farblos]

Thanks for the pointer, I wasn't aware of that other repo/issue. I have subscribed to the other issue, so feel free to close this one ...