agent: Return ToolResult from run inside Tool (#28763)

This is just a refactor which adds no functionality.
We now return a `ToolResult` from `Tool > run(...)`. For now this just
wraps the output task in a struct. We'll use this to implement custom
rendering of tools, see #28621.

Release Notes:

- N/A

crates/assistant_tools/src/delete_path_tool.rs

@@ -1,6 +1,6 @@
 use crate::schema::json_schema_for;
 use anyhow::{Result, anyhow};
-use assistant_tool::{ActionLog, Tool};
+use assistant_tool::{ActionLog, Tool, ToolResult};
 use futures::{SinkExt, StreamExt, channel::mpsc};
 use gpui::{App, AppContext, Entity, Task};
 use language_model::{LanguageModelRequestMessage, LanguageModelToolSchemaFormat};
@@ -63,15 +63,16 @@ impl Tool for DeletePathTool {
         project: Entity<Project>,
         action_log: Entity<ActionLog>,
         cx: &mut App,
-    ) -> Task<Result<String>> {
+    ) -> ToolResult {
         let path_str = match serde_json::from_value::<DeletePathToolInput>(input) {
             Ok(input) => input.path,
-            Err(err) => return Task::ready(Err(anyhow!(err))),
+            Err(err) => return Task::ready(Err(anyhow!(err))).into(),
         };
         let Some(project_path) = project.read(cx).find_project_path(&path_str, cx) else {
             return Task::ready(Err(anyhow!(
                 "Couldn't delete {path_str} because that path isn't in this project."
-            )));
+            )))
+            .into();
         };
 
         let Some(worktree) = project
@@ -80,7 +81,8 @@ impl Tool for DeletePathTool {
         else {
             return Task::ready(Err(anyhow!(
                 "Couldn't delete {path_str} because that path isn't in this project."
-            )));
+            )))
+            .into();
         };
 
         let worktree_snapshot = worktree.read(cx).snapshot();
@@ -132,5 +134,6 @@ impl Tool for DeletePathTool {
                 )),
             }
         })
+        .into()
     }
 }