simplicity sys: prepare simplicity-sys 0.8.0 release

[KyrylR]

TL;DR: we are bumping because of braking change of bitcoin_hashes dep

Ran the vendor command with the following command:

nix shell nixpkgs#gnused nixpkgs#coreutils \                      
  --command bash ./vendor-simplicity.sh \
  ./depend /tmp/simplicity-vendor-check.PIsQKe/upstream

On this revision of Simplicity: BlockstreamResearch/simplicity@ba967b1

It is my first time doing such bump, so I am not entirely convinced that it is necessary, but AI reasoning (which is below) looks legit to me

Summary by GPT-6 Astra

Bump simplicity-sys to 0.8.0 ahead of the next Rust Simplicity release

The hash dependency update moved bitcoin_hashes from 0.14 to 1.x. Since simplicity-sys exposes these types in its public API, this is a breaking change and requires a version bump

Update the versioned C symbols, corresponding Rust bindings, and Cargo linking metadata to the 0.8 namespace. Update the workspace dependency requirements and lockfile accordingly. The vendored Simplicity revision and C implementation remain unchange

Verified that rerunning the vendoring script produces no Git diff