Upgrade to NU5 testnet 2 versions of librustzcash, zcash_script, orchard, halo2_proofs

Motivation

Currently, Zebra and zcash_script depend on a git version of the following shared Zcash crates:

And we depend on pre-NU5 versions of:

We need to update to the NU5 testnet 2 versions of these crates.

Wait until the zcashd team releases 4.7.0, with the NU5 testnet 2 versions of librustzcash and orchard

Try:

halo2 = { package = "halo2_proofs", version = "=0.1.0-beta.2" }

"and then you only need to focus on the API changes, not renaming the imports everywhere."

See also the changelog for `halo2_proofs 0.1.0-beta.2 for all of the API changes relevant to this upgrade.

(This was a separate ticket before, for reference: #3600)

In the next steps, update zcash_script and Zebra to the latest git commit of zcash/librustzcash/master

Merge zcash/librustzcash/master into ZcashFoundation/librustzcash/download-sprout-params
Tag ZcashFoundation/librustzcash/download-sprout-params as a beta release, so zcash_script and Zebra can depend on it

Upgrade zcash_script to the NU5 testnet 2 orchard and librustzcash, removing the git versions in Cargo.toml
Revert module structure changes if needed: https://github.com/ZcashFoundation/zcash_script/pull/27
Remove the git patches in zcash_script/Cargo.toml
Merge the upgrade and module structure PRs to zcash_script/master
Tag a zcash_script beta release

Upgrade Zebra to the NU5 testnet 2 orchard and librustzcash, removing the git versions in Cargo.toml
Upgrade Zebra to the latest version ofzcash_script (git tag)
Remove the exceptions for orchard, librustzcash, and dependencies in deny.toml
Merge the Zebra upgrade PR along with the PR for ticket #3018