Fix Fedora CI build by aligning srpc/tutorial CMake C++ standard with protobuf requirements

[Copilot]

The Fedora Actions job fails because rawhide’s protobuf headers require C++17 features, while srpc build paths were pinned to C++14. This updates the affected non-Windows CMake flags so Fedora can compile against current protobuf.

• Root cause addressed

  • Fedora rawhide pulls newer protobuf headers (std::is_same_v, if constexpr) that are incompatible with -std=c++14.

• Build config updates (minimal scope)

  • src/CMakeLists.txt: non-Windows CMAKE_CXX_FLAGS switched from -std=c++14 to -std=c++17.
  • tutorial/CMakeLists.txt: same non-Windows flag update for tutorial builds.

• Resulting behavior

  • Keeps existing build flow intact; only raises language level where Fedora compilation was failing.

# before
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -fPIC -pipe -std=c++14 -fno-exceptions")

# after
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -fPIC -pipe -std=c++17 -fno-exceptions")