Boundary mode: performance optimizations + boundary filter

Performance optimizations:
- Move TLSF allocator pool to PSRAM (frees ~170KB internal SRAM)
- Raise TCP_IF_MAX_CLIENTS from 4 to 8 in BOUNDARY_MODE
- Raise path_table_maxsize from 48 to 128, persist from 16 to 32
- Add -DNDEBUG to boundary build: compiles out TRACE/DEBUG macros
- Log level defaults to LOG_VERBOSE when NDEBUG defined
- Serial baud 115200 -> 921600 in BOUNDARY_MODE (reduces CPU blocking)

Previous changes included in this commit:
- Comprehensive boundary filter with transitive whitelisting (7 checks)
- destination_table erase+insert fix (std::map::insert no-overwrite bug)
- Backbone-to-backbone routing guard in next-hop forwarding
- KISS serial output disabled for boundary mode
- flash.py updates for boundary mode support

lib/microReticulum/src/Log.cpp

@@ -8,8 +8,11 @@
 
 using namespace RNS;
 
-//LogLevel _level = LOG_VERBOSE;
+#ifdef NDEBUG
+LogLevel _level = LOG_VERBOSE;
+#else
 LogLevel _level = LOG_TRACE;
+#endif
 //LogLevel _level = LOG_MEM;
 RNS::log_callback _on_log = nullptr;
 char _datetime[20];