[bug] Fix mise x cargo:eza not installing during run

Addresses a bug with `mise exec` where using an unversioned tool
reference causes the underlying binary to not be installed on first use.

Instead we treat an unqualified tool as having tool@latest and handle
that in the else clause.

src/toolset/builder.rs

@@ -93,6 +93,9 @@ impl ToolsetBuilder {
             for arg in args {
                 if let Some(tvr) = &arg.tvr {
                     arg_ts.add_version(tvr.clone(), Default::default());
+                } else {
+                    let tvr = ToolVersionRequest::new(arg.forge.clone(), "latest".into());
+                    arg_ts.add_version(tvr.clone(), Default::default());
                 }
             }
             ts.merge(arg_ts);