[nexus] add support for CLI testing (#13110)

This commit adds support for interacting with nodes via the CLI in the
Nexus simulation framework. This enables writing higher-level
integration tests that verify stack behavior and state through
standard CLI commands.

Key changes:
- Integrated `Cli::Interpreter` into the `Nexus::Node` class.
- Added `Node::InputCli()` to allow sending commands to a node with
  `printf`-style formatting.
- Implemented output capturing logic in `Node::HandleCliOutput()` to
  buffer and parse CLI responses into individual lines, stored in a
  `CliOutputArray`.
- Added helper methods to `CliOutputLine` for matching and validating
  the captured output.
- Added a new `cli_basic` Nexus test to demonstrate and validate the
  CLI interaction functionality.

tests/nexus/platform/nexus_node.cpp

@@ -37,10 +37,12 @@ namespace Nexus {
 
 Node::Node(void)
     : Platform(static_cast<Instance &>(*this))
+    , mCliInterpreter(static_cast<Instance *>(this), HandleCliOutput, this)
     , mX(0.0f)
     , mY(0.0f)
     , mLastParentId(0xffff)
 {
+    mCliInterpreter.SetPromptConfig(false);
 }
 
 void Node::Reset(void)
@@ -298,6 +300,109 @@ const char *Node::GetExtendedRoleString(void) const
     return roleStr;
 }
 
+//- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+// Cli
+
+Node::CliOutputLine &Node::CliOutputLine::operator=(const CliOutputLine &aOther)
+{
+    SuccessOrQuit(mLine.Set(aOther.mLine));
+    return *this;
+}
+
+Node::CliOutputLine &Node::CliOutputLine::operator=(CliOutputLine &&aOther)
+{
+    mLine.TakeFrom(aOther.mLine.Move());
+    return *this;
+}
+
+void Node::InputCli(const char *aFormat, ...)
+{
+    static constexpr uint16_t kMaxCommandSize = 256;
+
+    va_list      args;
+    char         command[kMaxCommandSize];
+    StringWriter writer(command, kMaxCommandSize);
+
+    va_start(args, aFormat);
+    writer.AppendVarArgs(aFormat, args);
+    VerifyOrExit(!writer.IsTruncated());
+
+    ClearCliOutput();
+    mCliInterpreter.ProcessLine(command);
+
+exit:
+    va_end(args);
+}
+
+int Node::HandleCliOutput(void *aContext, const char *aFormat, va_list aArguments)
+{
+    return static_cast<Node *>(aContext)->HandleCliOutput(aFormat, aArguments);
+}
+
+int Node::HandleCliOutput(const char *aFormat, va_list aArguments)
+{
+    uint16_t length;
+
+    // Generate output - determine number of chars written
+    length = mCliCurOutputLine.GetLength();
+
+    mCliCurOutputLine.AppendVarArgs(aFormat, aArguments);
+    VerifyOrQuit(!mCliCurOutputLine.IsTruncated());
+
+    length = mCliCurOutputLine.GetLength() - length;
+
+    // Search for `\n` and parse lines one by one
+
+    while (true)
+    {
+        char           lineString[CliOutputLine::kMaxLineSize];
+        char          *end;
+        CliOutputLine *lineEnrry;
+
+        SuccessOrQuit(StringCopy(lineString, mCliCurOutputLine.AsCString()));
+
+        end = AsNonConst(StringFind(lineString, '\n'));
+        VerifyOrExit(end != nullptr);
+
+        mCliCurOutputLine.Clear();
+        mCliCurOutputLine.Append("%s", end + 1);
+
+        *end = kNullChar;
+
+        if (end > &lineString[0])
+        {
+            end--;
+
+            if (*end == '\r')
+            {
+                *end = kNullChar;
+            }
+        }
+
+        // Push the full line into the `mCliOutputLines` array
+
+        lineEnrry = mCliOutputLines.PushBack();
+        VerifyOrQuit(lineEnrry != nullptr);
+
+        SuccessOrQuit(lineEnrry->mLine.Set(lineString));
+    }
+
+exit:
+    return static_cast<int>(length);
+}
+
+bool Node::IsCliOutputSuccess(void)
+{
+    bool isSuccess = false;
+
+    VerifyOrExit(mCliOutputLines.GetLength() > 0);
+    VerifyOrExit(mCliOutputLines.Back()->IsDone());
+    isSuccess = true;
+
+exit:
+    return isSuccess;
+}
+
 //----------------------------------------------------------------------------------------------------------------------
 
 void AllowLinkBetween(Node &aFirstNode, Node &aSecondNode)