[WIP] chore: upgrade getrandom, rand & remove old getrandom

[sranish]

Summary of Changes

• All direct uses now point to getrandom 0.3.4 via the getrandom_03 workspace alias, and rand is centralized in the workspace.
• There are no explicit getrandom = "0.2" entries in any Cargo.toml.
• Current tendermint/rand versions still depend on getrandom 0.2; bumping them alone won’t eliminate it.

Resolves #782

[oblique]

We still need getrandom v0.2 because a dependency of tendermint is using it. If we remove it from our Cargo.toml then WASM builds will fail. In order to keep only v0.3, the v0.2 should not be anywhere in the dependency tree.