[CASESession] refactoring and improving testability of Sigma1 sending and handling, and Sigma2 Sending (#36679)

* Removing networking bits from CASESession ParseSigma1 and creating EncodeSigma1

* integrating comments

* Refactoring HandleSigma1_and_SendSigma2 and functions called within it

* Adding Encrypted2 datalen check

* renaming variables

* Making Parsing and Encoding methods protected

* Converting TLV tags to enum class

* Making structs protected and making Unit Test inherit CASESession

* integrating comments

* Integrating comments in TestCASESession

* integrate comments on CASESession

* Integrating more comments

* Using a Variant for the NextStep logic in HandleSigma1, to either send a Sigma message or a status report

* fixing clang-tidy error

* more comments

* comments integration

Author: Alami-Amine

src/lib/support/CodeUtils.h

@@ -156,6 +156,33 @@
         }                                                                                                                          \
     } while (false)
 
+/**
+ *  @def ReturnErrorVariantOnFailure(expr)
+ *
+ *  @brief
+ *    This is for use when the calling function returns a Variant type. It returns a CHIP_ERROR variant with the corresponding error
+ *    code if the expression returns an error.
+ *
+ *  Example usage:
+ *
+ *  @code
+ *    ReturnErrorVariantOnFailure(NextStep, ParseSigma1(tlvReader, parsedSigma1));
+ *  @endcode
+ *
+ *  @param[in]  variantType   The Variant type that the calling function returns.
+ *  @param[in]  expr          An expression to be tested.
+
+ */
+#define ReturnErrorVariantOnFailure(variantType, expr)                                                                             \
+    do                                                                                                                             \
+    {                                                                                                                              \
+        auto __err = (expr);                                                                                                       \
+        if (!::chip::ChipError::IsSuccess(__err))                                                                                  \
+        {                                                                                                                          \
+            return variantType::Create<CHIP_ERROR>(__err);                                                                         \
+        }                                                                                                                          \
+    } while (false)
+
 /**
  *  @def ReturnLogErrorOnFailure(expr)
  *