perf: optimize get_filestorage_size

[uncle-lv]

The old get_filestorage_size get the size by len(file.read()) which triggers a read operation and consumes additional memory.
Old version:

def get_filestorage_size(file: FileStorage) -> int:
    size = len(file.read())
    file.stream.seek(0)
    return size

The new get_filestorage_size get the size by file.stream.getbuffer().nbytes which returns the number of bytes of the data directly without any extra overhead.
New version:

def get_filestorage_size(file: FileStorage) -> int:
    size: int = file.stream.getbuffer().nbytes  # type: ignore
    return size

[sloria]

Thanks!