Keep same-named MCP servers separate across environments (#60905)

## Why

MCP servers discovered on different executors can share a name. Resolving them by name alone exposes only one server and prevents tools and resources from being addressed independently.

## What changed

- Add the disabled-by-default `multi_environment_mcp` feature to expose environment-scoped servers, including multiple installations of the same plugin.
- Carry exact `McpServerKey` identities through catalogs, connections, tool calls, resources, and approval tracking. Give environment-scoped tools stable namespaces derived from their environment.
- Include `environment_id` in scoped resource listings and accept it in resource requests. Require it for environment-owned servers when multiple environments are selected.
- Preserve server ownership through hooks and use the owning environment's permissions for scoped elicitation review.

## Testing

Add coverage for same-named servers across environments, independent calls and approvals, resource selection, plugin discovery, and rejection of hook changes to the tool environment.

GitOrigin-RevId: 5593372b06a15c16aa3220faa3b19f5d3b20e67e

codex-rs/core-plugins/src/executor_hooks_tests.rs

@@ -401,7 +401,7 @@ fn resolves_apps_hook_metadata_from_the_registered_connector() {
             |server, tool| {
                 tool_info
                     .as_ref()
-                    .filter(|info| info.server_name == server && info.tool.name == tool)
+                    .filter(|info| info.server_name() == server && info.tool.name == tool)
             },
         );
         let expected = if admitted {