Fix linter warnings · cda-tum/mtct@70286de

Process completed with exit code 1.

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L22

no header providing "size_t" is directly included

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L34

unchecked access to optional value

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L34

no header providing "GRB_CONTINUOUS" is directly included

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L35

no header providing "std::to_string" is directly included

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L37

unchecked access to optional value

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L45

unchecked access to optional value

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L46

no header providing "GRB_BINARY" is directly included

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L48

unchecked access to optional value

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L92

unchecked access to optional value

Run cpp-linter: src/solver/mip-based/VSSGenTimetableSolver_fixedRoutes.cpp#L99

unchecked access to optional value

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