feat(PPO_Bot): persist Adam optimizer state and round counter across restarts (#35)

Save ACAdamStates (m/v tensors + t counters) as .npy files alongside
network weights in latest/ and checkpoint dirs; save round counter to
round_counter.txt. loadBestAvailable restores both on startup; fresh
start works unchanged when files are absent.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

PPO_Bot/PPO_Bot.nim

@@ -57,7 +57,7 @@ proc trainingThreadProc(args: TrainingArgs) {.thread.} =
   var localAc = args.ac
   var localAdam = args.adamStates
   let m = ppoUpdate(localAc, args.buffer, lastValue = args.lastValue, adamStates = localAdam)
-  saveCheckpoint(localAc, args.weightsRoot, args.roundNum)
+  saveCheckpoint(localAc, localAdam, args.weightsRoot, args.roundNum)
   resultChan.send(TrainingResult(ac: localAc, adamStates: localAdam, metrics: m))
 
 # ── Bot methods ───────────────────────────────────────────────────────────────
@@ -219,7 +219,9 @@ when isMainModule:
   resultChan.open()
   createDir(weightsRoot)
   cleanStaleTempDirs(weightsRoot)
-  discard loadBestAvailable(ac, weightsRoot)
+  let loadResult = loadBestAvailable(ac, gAdamStates, weightsRoot)
+  if loadResult.loaded:
+    roundCounter = loadResult.roundNum
 
   var bot = PPOBot(
     tracker: initEnemyTracker(),