As mentioned in https://github.com/elastic/elasticsearch/pull/96216, `LuceneVerifyingIndexOutput` always copies the last chunk byte-by-byte. This might be a pretty big chunk. We should be able to copy all the bytes up to the start of the checksum in bulk (and then I guess bulk-copy the checksum too not that this matters so much).

In the same area, `LuceneVerifyingIndexOutput` is the only subclass of `VerifyingIndexOutput` and there's no need for it to be an inner class of `Store`. `VerifyingIndexInput` also doesn't need to be an inner class.
server/src/test/java/org/elasticsearch/index/store/StoreTests.java
for (int i = 0; i < iters; i++) {
                BytesRef bytesRef = new BytesRef(TestUtil.randomRealisticUnicodeString(random(), 10, 1024));
                output.writeBytes(bytesRef.bytes, bytesRef.offset, bytesRef.length);
                luceneFileLength += bytesRef.length;
            }
            CodecUtil.writeFooter(output);
            luceneFileLength += CodecUtil.footerLength();
        }
        try (IndexInput indexInput = dir.openInput("lucene_checksum.bin", IOContext.DEFAULT)) {
            assertEquals(luceneFileLength, indexInput.length());
        }
        dir.close();
    }
    public void testVerifyingIndexInput() throws IOException {
        Directory dir = newDirectory();
        IndexOutput output = dir.createOutput("foo.bar", IOContext.DEFAULT);
        int iters = scaledRandomIntBetween(10, 100);
        for (int i = 0; i < iters; i++) {
            BytesRef bytesRef = new BytesRef(TestUtil.randomRealisticUnicodeString(random(), 10, 1024));
            output.writeBytes(bytesRef.bytes, bytesRef.offset, bytesRef.length);
        }
        CodecUtil.writeFooter(output);
        output.close();
        
        IndexInput indexInput = dir.openInput("foo.bar", IOContext.DEFAULT);
        long checksum = CodecUtil.retrieveChecksum(indexInput);
        indexInput.seek(0);
        IndexInput verifyingIndexInput = new Store.VerifyingIndexInput(dir.openInput("foo.bar", IOContext.DEFAULT));
        readIndexInputFullyWithRandomSeeks(verifyingIndexInput);
        Store.verify(verifyingIndexInput);