build: add overflow-checks to governance code

[conorsch]

Based on one of the security audits in 2024Q3, we want to add overflow checks to the penumbra-governance crate. We can do this via a minimal diff to the workspace Cargo.toml file:

--- a/Cargo.toml
+++ b/Cargo.toml
@@ -85,6 +85,12 @@ x86_64-unknown-linux-gnu = "buildjet-32vcpu-ubuntu-2204"
 [profile.dist]
 inherits = "release"

+[profile.dev.package.penumbra-governance]
+overflow-checks = true
+
+[profile.release.package.penumbra-governance]
+overflow-checks = true
+
 # config for 'cargo release'
 [workspace.metadata.release]
 # Instruct cargo-release to increment versions for all packages in the workspace in lockstep.

This change was originally submitted as a PR in #4860, but due to its consensus-breaking nature, we opted not to merge it into the v0.80.x release series. When planning the next protocol upgrade, we should revisit this patch, and include it then, with appropriate documentation.

[aubrika]

Kicking this out of this sprint to potentially include in a future upgrade

[hdevalence]

I don't think we should plan to do this, ever -- the consensus-critical logic shouldn't be determined by build flags. Instead, if there is critical logic, it should use checked operations.

[redshiftzero]

OK we can use checked operations instead of doing the crate-wide overflow-checks. Closing this one