perf: fix slice boundary panics, eliminate string allocation in stdio reader, fix lua table nesting bug, and optimize nvim socket chunk size

stub/src/main.rs

@@ -98,7 +98,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                                 ">>> [Stub] Forwarding {} to server (length: {}): {}{}",
                                 log_prefix,
                                 msg.len(),
-                                &msg[..std::cmp::min(msg.len(), 1000)],
+                                &msg[..msg.floor_char_boundary(1000)],
                                 if msg.len() > 1000 { "..." } else { "" }
                             );
                             if write
@@ -120,7 +120,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                                     "<<< [Stub] Received {} from server (length: {}): {}{}",
                                     log_prefix,
                                     text.len(),
-                                    &text[..std::cmp::min(text.len(), 1000)],
+                                    &text[..text.floor_char_boundary(1000)],
                                     if text.len() > 1000 { "..." } else { "" }
                                 );
                                 use tokio::io::AsyncWriteExt;