OOM hardening and memory tuning

[attermann]

• Transport::inbound(): pre-emptive cull before destination-table insert;
  try/catch around insert for explicit OOM diagnostics
• Transport::jobs(): split stale-entry culling into 5 independent
  per-phase try/catch blocks so a failure in one phase doesn't abort
  the others; reserve() before push_back loops in each phase
• cull_path_table()/cull_known_destinations(): std::min_element fallback
  when sort-index allocation fails, breaking the cull-OOM-still-full loop
• Identity::remember(): wrapped _known_destinations.insert in try/catch
  for explicit OOM diagnostic logging
• Destination::announce(): outer try/catch covers all OOM-prone ops
  (Bytes concat, sign, Packet ctor, send); inner _path_responses.insert
  catch preserved for degraded-mode behavior
• Packet::unpack(): dedicated std::bad_alloc catch returns false cleanly
• Type.h: MAX_RECEIPTS and MAX_QUEUED_ANNOUNCES now overridable at
  compile time via RNS_RECEIPTS_MAX / RNS_QUEUED_ANNOUNCES_MAX
• Transport.h: hashlist_maxsize and max_pr_tags exposed as runtime
  accessors for dynamic capacity tuning
• Added more defines for setting storage and persistence limits (RNS_RATE_TIMESTAMPS_MAX, RNS_RANDOM_BLOBS_PERSIST_MAX, RNS_RANDOM_BLOBS_MAX)