fix: suppress new clippy lints for Rust 1.93

- Allow self_only_used_in_recursion in gantt.rs and mermaid.rs
- Allow private_interfaces in wasm schedule_internal method

These are intentional patterns: recursive methods keep &self for
consistency, and schedule_internal is pub for test visibility only.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: 2 people

crates/utf8proj-render/src/gantt.rs

@@ -391,6 +391,7 @@ impl HtmlGanttRenderer {
         result
     }
 
+    #[allow(clippy::only_used_in_recursion)]
     fn collect_tasks<'a>(
         &self,
         tasks: &'a [Task],

crates/utf8proj-render/src/mermaid.rs

@@ -270,6 +270,7 @@ impl Renderer for MermaidRenderer {
 
 impl MermaidRenderer {
     /// Collect first predecessor for each task
+    #[allow(clippy::only_used_in_recursion)]
     fn collect_predecessors(
         &self,
         task: &utf8proj_core::Task,

crates/utf8proj-wasm/src/lib.rs

@@ -736,6 +736,7 @@ impl Playground {
     ///
     /// This method is used by both the WASM binding and unit tests.
     /// Not exposed to WASM because Result<PlaygroundScheduleData, String> is not WASM-compatible.
+    #[allow(private_interfaces)]
     pub fn schedule_internal(
         &mut self,
         input: &str,