deb,cli,test,docs: record and show dep-install and build durations

Every binary build measures its dependency installation (apt-get
update, the essential and injected packages, each build-dependency
pass) and its package build (debian/rules build plus binary) into a
timings accumulator; the record manifest stores both as an optional
`timings` field when the run ends, whatever the outcome — a failed
build keeps its partial durations, and a run that died before any
timed command records nothing.

`pkh deb list` shows the two durations as DEPS and BUILD columns,
formatted like the age ("45s", "2m41s", "1h02m"); records predating
the field show dashes. The field is serde-optional, so the manifest
schema stays at 1 and existing records remain discoverable and
forkable.

src/test/mod.rs

@@ -561,7 +561,15 @@ async fn configure_testbed(
     }
 
     if !opts.inject.is_empty() {
-        crate::deb::local::install_injected_packages(&opts.inject, env, ctx.clone(), view, &None)?;
+        // Testbed setup is not a timed build: the durations go nowhere.
+        crate::deb::local::install_injected_packages(
+            &opts.inject,
+            env,
+            ctx.clone(),
+            view,
+            &None,
+            &mut crate::deb::session::BuildTimings::default(),
+        )?;
     }
     Ok(())
 }