remove the "@"-prefix from proof scripts

Author: wadoon

key.core/src/main/antlr4/KeYParser.g4

@@ -861,7 +861,7 @@ proofScriptEntry
 ;
 proofScriptEOF: proofScript EOF;
 proofScript: proofScriptCommand+;
-proofScriptCommand: AT? cmd=IDENT proofScriptParameters?
+proofScriptCommand: cmd=IDENT proofScriptParameters?
 	( LBRACE sub=proofScript RBRACE SEMI?
 	| SEMI);
 

key.core/src/main/java/de/uka/ilkd/key/macros/scripts/LetCommand.java

@@ -10,6 +10,8 @@
 import de.uka.ilkd.key.macros.scripts.meta.ProofScriptArgument;
 import de.uka.ilkd.key.nparser.KeYParser;
 import de.uka.ilkd.key.pp.AbbrevMap;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /// The *let* command lets you introduce entries to the abbreviation table.
 /// ```
@@ -22,6 +24,7 @@
 ///
 /// **Changes:**
 /// * Jan,2025 (weigl): add new parameter {@code force} to override bindings.
+@NullMarked
 public class LetCommand implements ProofScriptCommand<Map<String, Object>> {
 
     @Override

key.core/src/main/java/de/uka/ilkd/key/macros/scripts/ProofScriptEngine.java

@@ -132,9 +132,7 @@ public void execute(AbstractUserInterfaceControl uiControl,
             }
 
             final Node firstNode = stateMap.getFirstOpenAutomaticGoal().node();
-            if (commandMonitor != null
-                    && stateMap.isEchoOn()
-                    && commandContext.AT() == null) {
+            if (commandMonitor != null && stateMap.isEchoOn()) {
                 commandMonitor
                         .accept(new ExecuteInfo(cmd, start, firstNode.serialNr()));
             }
@@ -148,7 +146,7 @@ public void execute(AbstractUserInterfaceControl uiControl,
                 }
 
                 Object o = command.evaluateArguments(stateMap, argMap);
-                if (commandContext.AT() == null && stateMap.isEchoOn()) {
+                if (stateMap.isEchoOn()) {
                     LOGGER.debug("[{}] goal: {}, source line: {}, command: {}", ++cnt,
                         firstNode.serialNr(), commandContext.start.getLine(), cmd);
                 }
@@ -190,8 +188,7 @@ public void execute(AbstractUserInterfaceControl uiControl,
 
 
     public static String prettyPrintCommand(KeYParser.ProofScriptCommandContext ctx) {
-        return (ctx.AT() != null ? "@ " : "") +
-            ctx.cmd.getText() +
+        return ctx.cmd.getText() +
             (ctx.proofScriptParameters() != null
                     ? " " + ctx.proofScriptParameters().proofScriptParameter().stream()
                             .map(RuleContext::getText)