feat(test_framework): use TR_SAMPLE_BOTS env var for external bot directory

Adds TR_SAMPLE_BOTS env var support to point to external sample bots (Walls, Fire, SpinBot, etc). Updates test_bullet_economy.nim to use Walls from the sample-bots directory instead of custom WallsBot, removing the hardcoded path dependency.

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

common_libs/test_framework/test_framework.nim

@@ -12,10 +12,10 @@ export battle_result.RoundResult
 export battle_result.BotRoundResult
 
 proc runBattle*(botDirs: seq[string], rounds: int = 10,
-                timeout: int = 120000): BattleResult =
+                timeout: int = 120000, maxSpeed: bool = true): BattleResult =
   ensureServer()
   discard compileBots(botDirs)
-  let stdout = runBattleRunner(getServerUrl(), botDirs, rounds, timeout)
+  let stdout = runBattleRunner(getServerUrl(), botDirs, rounds, timeout, maxSpeed)
   result = parseServerOutput(stdout)
 
 when isMainModule:
@@ -26,7 +26,8 @@ when isMainModule:
   echo "  let r = runBattle(@[\"path/to/BotA\", \"path/to/BotB\"])"
   echo "  echo r.winners"
   echo ""
-  echo "Env vars forwarded to sub-modules:"
+  echo "Env vars:"
   echo "  TR_SERVER_JAR         TR server JAR path"
   echo "  TR_BATTLE_RUNNER      BattleRunner JAR path"
   echo "  TR_BATTLE_RUNNER_DIR  BattleRunner class dir"
+  echo "  TR_SAMPLE_BOTS        Directory containing sample bots (e.g. Walls, Fire, SpinBot)"