Add warning log when multiple checksum headers found in trailer

- Log a warning when multiple valid checksum headers appear in trailers
- Uses last checksum header as suggested by CodeRabbit reviewer
- Improves debugging for edge cases with multiple checksum algorithms

weed/s3api/chunked_reader_v4.go

@@ -530,6 +530,9 @@ func parseChunkChecksum(b *bufio.Reader) (ChecksumAlgorithm, []byte, error) {
 			key := string(parts[0])
 			value := trimTrailingWhitespace(parts[1])
 			if alg, err := extractChecksumAlgorithm(key); err == nil {
+				if checksumAlgorithm != ChecksumAlgorithmNone {
+					glog.V(3).Infof("multiple checksum headers found in trailer, using last: %s", key)
+				}
 				checksumAlgorithm = alg
 				checksum = value
 			}