assistant_tools: Reduce allocations (#30776)

Another batch of allocation savings. Noteworthy ones are
`find_path_tool.rs` where one clone of *all* found matches was saved and
`web_tool_search.rs` where the tooltip no longer clones the entire url
on every hover.

I'd also like to propose using `std::borrow::Cow` a lot more around the
codebase instead of Strings. There are hundreds if not 1000+ clones that
can be saved pretty regularly simply by switching to Cow. ´Cow´'s are
likely not used because they aren't compatible with futures and because
it could cause lifetime bloat. However if we use `Cow<'static, str>`
(static lifetime) for when we need to pass them into futures, we could
save a TON of allocations for `&'static str`. Additionally I often see
structs being created using `String`'s just to be deserialized
afterwards, which only requires a reference.

Release Notes:

- N/A

crates/assistant_tools/src/web_search_tool.rs

@@ -166,7 +166,7 @@ impl ToolCard for WebSearchToolCard {
                     .gap_1()
                     .children(response.results.iter().enumerate().map(|(index, result)| {
                         let title = result.title.clone();
-                        let url = result.url.clone();
+                        let url = SharedString::from(result.url.clone());
 
                         Button::new(("result", index), title)
                             .label_size(LabelSize::Small)