clang-tidy: replace costly string concatenation with stream construction

alib2abstraction/src/registry/AlgorithmRegistry.cpp

alib2abstraction/src/registry/CastRegistry.cpp

alib2abstraction/src/registry/ContainerRegistry.cpp

alib2abstraction/src/registry/NormalizeRegistry.cpp

alib2abstraction/src/registry/OperatorRegistry.cpp

alib2abstraction/src/registry/ValuePrinterRegistry.cpp

alib2std/src/extensions/sstream.h

tests/cppaql/approximateMatching.cpp

tests/cppaql/arbologyTest.cpp

tests/cppaql/conversionsTest.cpp

tests/cppaql/conversionsTest2.cpp

tests/cppaql/determinizeTest.cpp

tests/cppaql/exactMatching.cpp

tests/cppaql/glushkovRteTest.cpp

tests/cppaql/minimizeTest.cpp

tests/cppaql/normalizeTest.cpp

tests/cppaql/readerTest.cpp

tests/cppaql/regexpDerivationIntegralTest.cpp

tests/cppaql/regexpOptimizeTest.cpp

tests/cppaql/treeNotationTest.cpp