Build with Stable! Also, update to Risc0 v0.18.

[preston-evans98]

Description

This PR updates to Risc0 v0.18, which allows Sovereign to switch to the stable toolchain! 🎉

Linked Issues

• Fixes Sovereign SDK should work with stable rust #29
• Related to Build with Stable; Add Stable to CI #11 Update to risc0 v0.17 #765 Bump risc0-zkvm-platform from 0.16.1 to 0.18.0 #861

Testing

These changes are covered by existing tests

[codecov]

Codecov Report

Merging #869 (35efb02) into nightly (177d989) will increase coverage by 0.0%.
The diff coverage is 0.0%.

Files Changed	Coverage Δ
adapters/risc0/src/host.rs	18.3% <0.0%> (+1.4%)	⬆️
module-system/sov-modules-macros/src/cli_parser.rs	95.0% <0.0%> (+0.5%)	⬆️
utils/zk-cycle-utils/src/lib.rs	0.0% <0.0%> (ø)

... and 2 files with indirect coverage changes