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.
- Add cull_announce_table() with OOM-safe min_element fallback, matching pattern from cull_path_table() and cull_known_destinations()
- Call cull immediately after every announce/path/known-destination insert
- Fix use-after-free: guard announce_entry access with announce_erased flag
- remove_path() now also deletes cached packet files
- Path table insert now removes existing entry first to prevent duplicates
- Rename env:mcu -> env:embedded; add env:native_debug and heltec_wifi_lora_32_V4
- Make TLSF buffer size configurable via RNS_TLSF_BUFFER_SIZE macro
- Refactor log macros to unified RNS::log() path; add doHeadLog with callback support
- Prefix all bad_alloc error messages with "bad_alloc -" for easier grepping
