Update fenwick requirement from 1.0.0 to 2.0.0 (#38)

Updates the requirements on [fenwick](https://github.com/summivox/fenwick.rs) to permit the latest version.
- [Release notes](https://github.com/summivox/fenwick.rs/releases)
- [Commits](https://github.com/summivox/fenwick.rs/commits)

---
updated-dependencies:
- dependency-name: fenwick
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

fenwick-model/Cargo.toml

@@ -12,5 +12,5 @@ repository = "https://github.com/danieleades/arithmetic-coding"
 
 [dependencies]
 arithmetic-coding-core = { path = "../arithmetic-coding-core" }
-fenwick = "1.0.0"
+fenwick = "2.0.0"
 thiserror = "1.0.30"