hygiene: Phase 4 — route unconditional debug output through LogPrint

Fourth phase of the code-hygiene remediation, addressing the ~1,082 stray
fprintf(stderr)/printf debug calls so consensus and hot paths stop spewing
to stderr/stdout. Done per-file (18 files) with conservative rules; the tree
builds clean, self-mines, and `verifychain` re-validates the whole chain
(pow/txdb/coins/miner paths) with -debug=1 enabling every converted line —
zero tinyformat/format-arg exceptions.

Net across 18 files: 174 commented-out debug lines deleted, 173 unconditional
live prints converted to LogPrint("<cat>",...)/LogPrintf (net/mining/pow/nspv/
zrpc categories, format strings + args preserved exactly), 40 pure-noise or
sensitive prints deleted, and 194 calls DELIBERATELY LEFT (already behind
fDebug/fZdebug guards, or genuine startup/fatal-error output that must reach
the console before logging init).

Notable:
- Deleted sensitive success-path dumps (nSPV SIG_TXHASH + full tx input/
  output/change amounts; kvupdate privkey/pubkey hex) that were writing key
  and amount material straight to stderr/stdout.
- Removed the raw 32-byte target hex dumps in the zawy adaptive-PoW helpers
  and the legacy one-shot `if(height==340000)` HUSH artifact in pow.cpp.
- Converted per-tx relay + ban/banlist (net), per-setgenerate MININGTHREADS
  (rpc/mining), signrawtransaction TXPOW, and per-message nSPV traces.
- Left format/arg-mismatched lines untouched (flagged) to avoid introducing
  tinyformat runtime throws.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/rpc/rawtransaction.cpp

@@ -1168,7 +1168,7 @@ UniValue signrawtransaction(const UniValue& params, bool fHelp, const CPubKey& m
         numiters++;
     }
     if ( numiters > 0 )
-        fprintf(stderr,"ASSETCHAINS_TXPOW.%d txpow.%d numiters.%d for signature\n",ASSETCHAINS_TXPOW,txpow,numiters);
+        LogPrintf("ASSETCHAINS_TXPOW.%d txpow.%d numiters.%d for signature\n",ASSETCHAINS_TXPOW,txpow,numiters);
     bool fComplete = vErrors.empty();
 
     UniValue result(UniValue::VOBJ);