Converted log calls across src/, examples/, and test/ to use DEBUGF/TRACEF/ERRORF/etc. macros instead of std::string + operator+. This eliminates temporary heap allocations on every log call, which matters on memory-constrained MCUs.
Added support for new `context_flag` in RNS packet header that is used
to indicate the use of ratchets.
Note that ratchet support is still missing from the implementation, but
this fix enables received ratchets to be able to handled gracefully.
