rust-config: demonstrate a bug when falling back to non-trivial default values The default value (when the user hasn't configured anything) is not run through the value parser, causing a programming error to happen because of type mismatch. This will be fixed in the next commit.

rust: make `Revision` a newtype This change is the one we've been building towards during this series. The aim is to make `Revision` mean more than a simple integer, holding the information that it is valid for a given revlog index. While this still allows for programmer error, since creating a revision directly and querying a different index with a "checked" revision are still possible, the friction created by the newtype will hopefully make us think twice about which type to use. Enough of the Rust ecosystem relies on the newtype pattern to be efficiently optimized away (even compiler in codegen tests¹), so I'm not worried about this being a fundamental problem. [1] https://github.com/rust-lang/rust/blob/7a70647f195f6b0a0f1ebd72b1542ba91a32f43a/tests/codegen/vec-in-place.rs#L47

rust: implement the `Graph` trait for all revlogs This is trivial and makes all the algorithms relying on the trait usable for more use cases.