fix: flush TextDecoder on stream end to prevent silent data loss

When using decoder.decode(value, { stream: true }), the TextDecoder may
hold incomplete multi-byte UTF-8 bytes internally. Without flushing on
EOF, those trailing bytes were silently dropped — a regression from the
previous behavior which would at minimum emit replacement characters.

Author: beran-t

js/src/utils.ts

@@ -30,6 +30,8 @@ export async function* readLines(stream: ReadableStream<Uint8Array>) {
       const { done, value } = await reader.read()
 
       if (done) {
+        const trailing = decoder.decode()
+        if (trailing) pending.push(trailing)
         if (pending.length > 0) {
           yield pending.join('')
         }