rust: add `Progress` trait for progress bars

This will be used in the next few changes to introduce a progress bar for
the `hg update` fastpath.

rust/hg-core/src/progress.rs

@@ -0,0 +1,11
+//! Progress-bar related things
+
+/// A generic determinate progress bar trait
+pub trait Progress: Send + Sync + 'static {
+    /// Set the current position and optionally the total
+    fn update(&self, pos: u64, total: Option<u64>);
+    /// Increment the current position and optionally the total
+    fn increment(&self, step: u64, total: Option<u64>);
+    /// Declare that progress is over and the progress bar should be deleted
+    fn complete(self);
+}

rust/hg-core/src/lib.rs

@@ -35,6 +35,7 pub mod config;
 pub mod lock;
 pub mod logging;
 pub mod operations;
+pub mod progress;
 pub mod revset;
 pub mod utils;
 pub mod vfs;