Size & CRC in dfu-start; topic-reader stop-from-callback crashes

[maloel]

Size and CRC are currently not an input.
FW size is not known in advance.

5e needs to know how much memory to allocate before reading from the dfu topic, so the size needs to be communicated in advance for the allocation.

The CRC was added as well, to aid in validating that the blob was received intact.

• While doing this, a problem surfaced during testing: quitting DFU from a side thread (as the adapter does, e.g. in case of error) crashed
  • This was because we were destroying the reader from within a callback from the reader
  • Revised dds_topic_reader to use shared_from_this() to keep the object alive; made _stopped a shared_ptr to share ownership
  • Code that relied on the reader dtor stopping the reader needed changing: we can no longer count on the object to be destroyed so must (correctly) specify the intent (stopping) on destruction

I also simplified the DDS tests a bit.

Tracked on [RSDEV-1869]