More efficient copy object (#6665)

* it compiles

* refactored

* reduce to 4 concurrent chunk upload

* CopyObjectPartHandler

* copy a range of the chunk data, fix offset size in copied chunks

* Update s3api_object_handlers_copy.go

What the PR Accomplishes:
CopyObjectHandler - Now copies entire objects by copying chunks individually instead of downloading/uploading the entire file
CopyObjectPartHandler - Handles copying parts of objects for multipart uploads by copying only the relevant chunk portions
Efficient Chunk Copying - Uses direct chunk-to-chunk copying with proper volume assignment and concurrent processing (limited to 4 concurrent operations)
Range Support - Properly handles range-based copying for partial object copies

* fix compilation

* fix part destination

* handling small objects

* use mkFile

* copy to existing file or part

* add testing tools

* adjust tests

* fix chunk lookup

* refactoring

* fix TestObjectCopyRetainingMetadata

* ensure bucket name not conflicting

* fix conditional copying tests

* remove debug messages

* add custom s3 copy tests

weed/s3api/filer_multipart.go

@@ -93,7 +93,7 @@ func (s3a *S3ApiServer) completeMultipartUpload(input *s3.CompleteMultipartUploa
 			completedPartNumbers = append(completedPartNumbers, part.PartNumber)
 		}
 		completedPartMap[part.PartNumber] = append(completedPartMap[part.PartNumber], part.ETag)
-		maxPartNo = max(maxPartNo, part.PartNumber)
+		maxPartNo = maxInt(maxPartNo, part.PartNumber)
 	}
 	sort.Ints(completedPartNumbers)
 
@@ -444,3 +444,11 @@ func (s3a *S3ApiServer) listObjectParts(input *s3.ListPartsInput) (output *ListP
 
 	return
 }
+
+// maxInt returns the maximum of two int values
+func maxInt(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}