Update dependencies, require libsodium

[alexheretic]

• Update thrussh to 0.35.6, remove dependency pinning. This means we now require libsodium at build & runtime.
• Update reqwest to 0.12
• Update smol_str to 0.3
• Update parse_link_header to 0.4
• Update toml to 0.8
• Update cargo_metadata to 0.18
• Update ustr to 1

While the libsodium requirement is a slight pain, it seems preferable to have up to date dependencies.

[w4]

Thanks. There is also a well maintained fork called russh that we've switched to internally. Really need to backport some of the patches we've made there.