rust-core: add missing `Debug` traits

rust-core: add missing `Debug` traits

Turns out you need them when trying to use `hg-core` as a library. Who knew.

Differential Revision: https://phab.mercurial-scm.org/D8278

--- a/rust/hg-core/src/dirstate/status.rs	Thu Dec 12 16:24:43 2019 -0800
+++ b/rust/hg-core/src/dirstate/status.rs	Fri Mar 13 00:41:22 2020 +0100
@@ -623,6 +623,7 @@
     );
 }
 
+#[derive(Debug)]
 pub struct DirstateStatus<'a> {
     pub modified: Vec<Cow<'a, HgPath>>,
     pub added: Vec<Cow<'a, HgPath>>,
@@ -679,6 +680,7 @@
     )
 }
 
+#[derive(Debug)]
 pub enum StatusError {
     IO(std::io::Error),
     Path(HgPathError),

--- a/rust/hg-core/src/lib.rs	Thu Dec 12 16:24:43 2019 -0800
+++ b/rust/hg-core/src/lib.rs	Fri Mar 13 00:41:22 2020 +0100
@@ -103,6 +103,7 @@
     }
 }
 
+#[derive(Debug)]
 pub enum DirstateError {
     Parse(DirstateParseError),
     Pack(DirstatePackError),