fix: Generate Dafny 4.6 version of SimpleString patch for Rust (#345)

Fixes nightly build failure: https://github.com/smithy-lang/smithy-dafny/actions/runs/8804008273/job/24163426403.

Dry run of nightly build against this branch: https://github.com/smithy-lang/smithy-dafny/actions/runs/8819703065

Using 4.5.0 instead of 4.6.0 because Dafny uses version suffixes slightly wrong: nightlies will have version numbers like 4.6.0-nightly-2024-04-22-0082cf6 which by NuGet semantics means "a prerelease for the upcoming 4.6.0 release", and is therefore considered less than 4.6.0.