Misleading naming on `Program::with_pub_key`

[stringhandler]

Simplex version

0

What happened?

The method with_pub_key is actually the public key used for the taproot tweak, which a user may mistake for another public key referenced in the simplicity program, especially when there is only one public key in the program or if there is a parameter named param::PUBLIC_KEY.

I suggest naming it something more descriptive so that errors can be picked up at a quick glance during code reviews.

Possibly with_taproot_tweak_key. Preferrably not with_internal_key which is also not very descriptive in it's use.

For completeness, I'd suggest adding a builder method with_unspendable_taproot_key() which resets it back to tr_unspendable_key, but this is not as important.

Minimal reproduction steps

Design bug

[apoelstra]

"tweak key" is nonstandard terminology and the word "tweak" is heavily overloaded in the bitcoin and elements spaces (so we have a multi-year project to stop using it :P).

So I'd be happy with with_taproot_internal_key or even just with_taproot_pubkey (I have no strong feelings on how many _s to use or "pubkey" vs "key".)

[stringhandler]

yeah, I'm happy with that