More strict tolerance for unit/integration tests

[sjsprecious]

One index bug in LuDecomposition is identified by @K20shores in #625 .

After the index bug is fixed, the tolerance used in the unit and integration tests is expected to be much small in magnitude.

Acceptance Criteria

• All tolerances are set to a value as low as possible for any test which in some way uses LU decomposition

Ideas

• Try lowering tolerances in these files
  • All the integration tests: test/integration
  • test/unit/solver/test_linear_solver_policy.hpp
    • Which is called from test/unit/solver/test_linear_solver.cpp and test/unit/jit/solver/test_jit_linear_solver.cpp and test/unit/cuda/solver/test_cuda_linear_solver.cpp
  • test/unit/solver/test_lu_decomposition_policy.hpp
    • Which is called from test/unit/solver/test_lu_decomposition.cpp and test/unit/jit/solver/test_jit_lu_decomposition.cpp and test/unit/cuda/solver/test_cuda_lu_decomposition.cpp