feat!: update C++ standard to C++20 (#149)

### Briefly, what does this PR introduce?
This PR upgrades minimum required C++ standard to C++20. Already
required for EICrecon, so no one will be cut off by this.

### What kind of change does this PR introduce?
- [ ] Bug fix (issue #__)
- [x] New feature (issue: modernization woohoo)
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
- [ ] Changes have been communicated to collaborators

### Does this PR introduce breaking changes? What changes might users
need to make to their code?
Yes, C++20 required.

### Does this PR change default behavior?
No.

Author: wdconinc

CMakeLists.txt

@@ -30,8 +30,8 @@ else()
 endif()
 
 # C++ standard
-set(CMAKE_CXX_STANDARD_MIN 17)
-set(CMAKE_CXX_STANDARD 17 CACHE STRING "Set the C++ standard to be used")
+set(CMAKE_CXX_STANDARD_MIN 20)
+set(CMAKE_CXX_STANDARD 20 CACHE STRING "Set the C++ standard to be used")
 if(CMAKE_CXX_STANDARD LESS CMAKE_CXX_STANDARD_MIN)
   message(
     FATAL_ERROR