ProtobufNativeSchema: convert abseil string_view to std::string

This resolves the following build failure using abseil-cpp 20250814.1:

```
[  1%] Building CXX object lib/CMakeFiles/PULSAR_OBJECT_LIB.dir/ProtobufNativeSchema.cc.o
cd /home/build/pulsar-client-cpp/build/lib && /usr/local/bin/c++ -DBOOST_ALLOW_DEPRECATED_HEADERS -DBOOST_ALL_NO_LIB -DBUILDING_PULSAR -DHAS_SNAPPY=0 -DHAS_ZSTD=0 -DPULSAR_AUXV_GETAUXVAL_PRESENT -I/home/build/pulsar-client-cpp -I/home/build/pulsar-client-cpp/include -I/home/build/pulsar-client-cpp/build/include -I/home/build/pulsar-client-cpp/build/generated -I/home/build/pulsar-client-cpp/build/generated/lib -Wno-array-bounds -O2 -g -DNDEBUG -std=gnu++17 -fPIC -Wall -Wformat-security -Wvla -Werror -Wno-sign-compare -Wno-deprecated-declarations -Wno-error=cpp -msse4.2 -mpclmul -fdiagnostics-show-option -fdiagnostics-color -fvisibility=hidden -MD -MT lib/CMakeFiles/PULSAR_OBJECT_LIB.dir/ProtobufNativeSchema.cc.o -MF CMakeFiles/PULSAR_OBJECT_LIB.dir/ProtobufNativeSchema.cc.o.d -o CMakeFiles/PULSAR_OBJECT_LIB.dir/ProtobufNativeSchema.cc.o -c /home/build/pulsar-client-cpp/lib/ProtobufNativeSchema.cc
/home/build/pulsar-client-cpp/lib/ProtobufNativeSchema.cc: In function 'pulsar::SchemaInfo pulsar::createProtobufNativeSchema(const google::protobuf::Descriptor*)':
/home/build/pulsar-client-cpp/lib/ProtobufNativeSchema.cc:42:67: error: invalid initialization of reference of type 'const std::string&' {aka 'const std::__cxx11::basic_string<char>&'} from expression of type 'absl::lts_20250814::string_view' {aka 'std::basic_string_view<char>'}
   42 |     const std::string& rootMessageTypeName = descriptor->full_name();
      |                                              ~~~~~~~~~~~~~~~~~~~~~^~
/home/build/pulsar-client-cpp/lib/ProtobufNativeSchema.cc:43:69: error: invalid initialization of reference of type 'const std::string&' {aka 'const std::__cxx11::basic_string<char>&'} from expression of type 'absl::lts_20250814::string_view' {aka 'std::basic_string_view<char>'}
   43 |     const std::string& rootFileDescriptorName = fileDescriptor->name();
      |                                                 ~~~~~~~~~~~~~~~~~~~~^~
make[2]: *** [lib/CMakeFiles/PULSAR_OBJECT_LIB.dir/build.make:1052: lib/CMakeFiles/PULSAR_OBJECT_LIB.dir/ProtobufNativeSchema.cc.o] Error 1
```

Signed-off-by: dann frazier <[email protected]>

Author: dannf

lib/ProtobufNativeSchema.cc

@@ -39,8 +39,8 @@ SchemaInfo createProtobufNativeSchema(const google::protobuf::Descriptor* descri
     }
 
     const auto fileDescriptor = descriptor->file();
-    const std::string& rootMessageTypeName = descriptor->full_name();
-    const std::string& rootFileDescriptorName = fileDescriptor->name();
+    const std::string& rootMessageTypeName = std::string(descriptor->full_name());
+    const std::string& rootFileDescriptorName = std::string(fileDescriptor->name());
 
     FileDescriptorSet fileDescriptorSet;
     internalCollectFileDescriptors(fileDescriptor, fileDescriptorSet);