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 (StoreFileMetadata md : first) {
            assertThat(second.get(md.name()), notNullValue());
            
            assertThat(second.get(md.name()).isSame(md), equalTo(false));
        }
        assertThat(diff.different.size(), equalTo(first.size()));
        assertThat(diff.identical.size(), equalTo(0)); 
        assertThat(diff.missing, empty());
        
        Store.RecoveryDiff selfDiff = first.recoveryDiff(first);
        assertThat(selfDiff.identical.size(), equalTo(first.size()));
        assertThat(selfDiff.different, empty());
        assertThat(selfDiff.missing, empty());
        
        final String deleteId = Integer.toString(random().nextInt(numDocs));
        Store.MetadataSnapshot metadata;
        {
            Random random = new Random(seed);
            IndexWriterConfig iwc = new IndexWriterConfig(new MockAnalyzer(random)).setCodec(TestUtil.getDefaultCodec());
            iwc.setMergePolicy(NoMergePolicy.INSTANCE);
            iwc.setUseCompoundFile(random.nextBoolean());
            iwc.setOpenMode(IndexWriterConfig.OpenMode.APPEND);
            IndexWriter writer = new IndexWriter(store.directory(), iwc);
            logger.info("--> delete doc {}", deleteId);
            writer.deleteDocuments(new Term("id", deleteId));
            writer.commit();
            writer.close();
            metadata = store.getMetadata(null);
        }
        StoreFileMetadata delFile = null;