cli: move $JJ_VERSION out of CLI library

It should be up to the binary to decide which version it is. One
should be able to build the library without specifying a version.

src/cli_util.rs

@@ -2294,6 +2294,12 @@ impl CliRunner {
         }
     }
 
+    /// Set the version to be displayed by `jj version`.
+    pub fn version(mut self, version: &'static str) -> Self {
+        self.app = self.app.version(version);
+        self
+    }
+
     /// Replaces `StoreFactories` to be used.
     pub fn set_store_factories(mut self, store_factories: StoreFactories) -> Self {
         self.store_factories = Some(store_factories);

src/commands/mod.rs

@@ -3473,8 +3473,7 @@ fn cmd_sparse(ui: &mut Ui, command: &CommandHelper, args: &SparseArgs) -> Result
 }
 
 pub fn default_app() -> Command {
-    let app: Command = Commands::augment_subcommands(Args::command());
+    Commands::augment_subcommands(Args::command())
-    app.version(env!("JJ_VERSION"))
 }
 
 pub fn run_command(

src/main.rs

@@ -15,5 +15,5 @@
 use jujutsu::cli_util::CliRunner;
 
 fn main() -> std::process::ExitCode {
-    CliRunner::init().run()
+    CliRunner::init().version(env!("JJ_VERSION")).run()
 }