Extract exec-server CLI startup into a dedicated module (#47143)

## What changed

Move `codex exec-server` argument definitions, transport validation, configuration loading, authentication, and shutdown orchestration from `codex-rs/cli/src/main.rs` into `codex-rs/cli/src/exec_server_command.rs`.

Expose startup through `ExecServerCommand::run`, merge the root `--strict-config` flag into the command before dispatch, and update existing argument tests to use the new entry point.

GitOrigin-RevId: 4bcc59db2bd6e1d153a366142bd0b93ad03c6951

codex-rs/cli/src/exec_server_args_tests.rs

@@ -2,6 +2,7 @@ use clap::error::ErrorKind;
 use pretty_assertions::assert_eq;
 
 use super::*;
+use crate::exec_server_command::ExecServerRemoteTransport;
 
 fn exec_server_from_args(args: &[&str]) -> ExecServerCommand {
     let cli = MultitoolCli::try_parse_from(
@@ -199,14 +200,13 @@ async fn exec_server_sigv4_does_not_enable_aws_auth_for_noise() {
         args.extend(options);
         let command = exec_server_from_args(&args);
         // Unset runtime paths prove validation runs before startup or credential loading.
-        let error = run_exec_server_command(
-            command,
-            &Arg0DispatchPaths::default(),
-            &CliConfigOverrides::default(),
-            /*strict_config*/ false,
-        )
-        .await
-        .expect_err("Noise auth is unchanged");
+        let error = command
+            .run(
+                &Arg0DispatchPaths::default(),
+                &CliConfigOverrides::default(),
+            )
+            .await
+            .expect_err("Noise auth is unchanged");
         assert_eq!(
             error.to_string(),
             "--aws-sigv4 requires --remote-transport direct"
@@ -250,14 +250,13 @@ async fn exec_server_direct_forwarding_remains_rejected() {
             "bedrock-mantle"
         ),
     );
-    let error = run_exec_server_command(
-        command,
-        &Arg0DispatchPaths::default(),
-        &CliConfigOverrides::default(),
-        /*strict_config*/ false,
-    )
-    .await
-    .expect_err("Direct forwarding is unsupported before startup");
+    let error = command
+        .run(
+            &Arg0DispatchPaths::default(),
+            &CliConfigOverrides::default(),
+        )
+        .await
+        .expect_err("Direct forwarding is unsupported before startup");
     assert_eq!(
         error.to_string(),
         "direct exec-server transport does not support forwarding"