assistant: Make scripting a first-class concept instead of a tool (#26338)

This PR makes refactors the scripting functionality to be a first-class
concept of the assistant instead of a generic tool, which will allow us
to build a more customized experience.

- The tool prompt has been slightly tweaked and is now included as a
system message in all conversations. I'm getting decent results, but now
that it isn't in the tools framework, it will probably require more
refining.

- The model will now include an `<eval ...>` tag at the end of the
message with the script. We parse this tag incrementally as it streams
in so that we can indicate that we are generating a script before we see
the closing `</eval>` tag. Later, this will help us interpret the script
as it arrives also.

- Threads now hold a `ScriptSession` entity which manages the state of
all scripts (from parsing to exited) in a centralized way, and will
later collect all script operations so they can be displayed in the UI.

- `script_tool` has been renamed to `assistant_scripting` 

- Script source now opens in a regular read-only buffer  

Note: We still need to handle persistence properly

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/scripting_tool/src/scripting_tool.rs

@@ -1,58 +0,0 @@
-mod session;
-
-use project::Project;
-pub(crate) use session::*;
-
-use assistant_tool::{Tool, ToolRegistry};
-use gpui::{App, AppContext as _, Entity, Task};
-use schemars::JsonSchema;
-use serde::Deserialize;
-use std::sync::Arc;
-
-pub fn init(cx: &App) {
-    let registry = ToolRegistry::global(cx);
-    registry.register_tool(ScriptingTool);
-}
-
-#[derive(Debug, Deserialize, JsonSchema)]
-struct ScriptingToolInput {
-    lua_script: String,
-}
-
-struct ScriptingTool;
-
-impl Tool for ScriptingTool {
-    fn name(&self) -> String {
-        "lua-interpreter".into()
-    }
-
-    fn description(&self) -> String {
-        include_str!("scripting_tool_description.txt").into()
-    }
-
-    fn input_schema(&self) -> serde_json::Value {
-        let schema = schemars::schema_for!(ScriptingToolInput);
-        serde_json::to_value(&schema).unwrap()
-    }
-
-    fn run(
-        self: Arc<Self>,
-        input: serde_json::Value,
-        project: Entity<Project>,
-        cx: &mut App,
-    ) -> Task<anyhow::Result<String>> {
-        let input = match serde_json::from_value::<ScriptingToolInput>(input) {
-            Err(err) => return Task::ready(Err(err.into())),
-            Ok(input) => input,
-        };
-
-        let session = cx.new(|cx| Session::new(project, cx));
-        let lua_script = input.lua_script;
-        let script = session.update(cx, |session, cx| session.run_script(lua_script, cx));
-        cx.spawn(|_cx| async move {
-            let output = script.await?.stdout;
-            drop(session);
-            Ok(format!("The script output the following:\n{output}"))
-        })
-    }
-}