CI, CMake: intel-serial

Description

• Add CMake job for intel-serial
• Compare results and runtime
• Disable corresponding autotools job

Noting that due to spack's configuration (@lang-m can elaborate), Intel is using the system standard lib for C. This is causing a linker (?) error with the C library, nlopt. As nlopt is only used in the optimal control module of Octopus, which is not a fundamental Octopus feature, and is test-covered by GCC, this MR sets it such that Intel DOES NOT run regression tests for optimal control.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.