fix: check rotate_segment return value; use uint32_t for CRC fields

- In persist_wal_async(), check rotate_segment() return value and propagate -EIO on failure (MEDIUM)
- Change last_crc and last_replicated_crc fields from uint64_t to uint32_t to match CRC32 width (LOW)

Both fixes address code review issues in commit b0a5fbb.

src/controller/persist.c

@@ -256,8 +256,12 @@ int persist_wal_async(persist_t* p, uint32_t type,
     p->last_replicated_crc  = hdr.crc;
 
     /* Rotate segment when full */
-    if (p->seg_offset >= WAL_SEGMENT_SIZE_BYTES)
-        rotate_segment(p);
+    if (p->seg_offset >= WAL_SEGMENT_SIZE_BYTES) {
+        if (rotate_segment(p) != 0) {
+            pthread_mutex_unlock(&p->lock);
+            return -EIO;
+        }
+    }
 
     pthread_mutex_unlock(&p->lock);
     return 0;

src/include/persist.h

@@ -89,8 +89,8 @@ struct persist_s {
     /* WAL state */
     int             wal_fd;
     uint64_t        current_lsn;
-    uint64_t        last_crc;
-    uint64_t        last_replicated_crc;
+    uint32_t        last_crc;
+    uint32_t        last_replicated_crc;
     uint64_t        term;
     uint32_t        seg_offset;
     uint64_t        checkpoint_lsn;