Failure to compile with Rust 1.75

When trying to use the new version with the Rust 1.75 compiler, I get the following error:
```
error[E0658]: use of unstable library feature 'error_in_core'
  --> arbitrary-1.4.0/src/lib.rs:52:6
   |
52 | impl core::error::Error for MaxRecursionReached {}
```

It looks like while `std::error::Error` has been around for a while, its presence in `core` is new as of Rust 1.81