Centralize sparsediffpy import into _bindings.py

[Transurgeon]

Move the duplicated try/except import of sparsediffpy from c_problem.py and converters.py into a single _bindings.py module.

Description

Please include a short summary of the change.
Issue link (if applicable):

Type of change

• New feature (backwards compatible)
• New feature (breaking API changes)
• Bug fix
• Other (Documentation, CI, ...)

Contribution checklist

• Add our license to new files.
• Check that your code adheres to our coding style.
• Write unittests.
• Run the unittests and check that they’re passing.
• Run the benchmarks to make sure your change doesn’t introduce a regression.

[github-actions]

Benchmarks that have improved:

   before           after         ratio
 [ce8fda13]       [3f54d9cb]

•     300±0ms          256±0ms     0.85  simple_QP_benchmarks.SimpleQPBenchmark.time_compile_problem
  

•     853±0ms          721±0ms     0.84  simple_QP_benchmarks.LeastSquares.time_compile_problem
  

•     1.37±0s          1.12±0s     0.82  gini_portfolio.Cajas.time_compile_problem
  

Benchmarks that have stayed the same:

   before           after         ratio
 [ce8fda13]       [3f54d9cb]
      492±0ms          524±0ms     1.06  semidefinite_programming.SemidefiniteProgramming.time_compile_problem
      13.3±0s          14.1±0s     1.06  finance.CVaRBenchmark.time_compile_problem
      1.53±0s          1.58±0s     1.03  tv_inpainting.TvInpainting.time_compile_problem
     37.7±0ms         38.4±0ms     1.02  matrix_stuffing.SmallMatrixStuffing.time_compile_problem
      286±0ms          291±0ms     1.02  matrix_stuffing.ParamSmallMatrixStuffing.time_compile_problem
      1.47±0s          1.49±0s     1.02  matrix_stuffing.ParamConeMatrixStuffing.time_compile_problem
      9.88±0s          10.0±0s     1.01  simple_LP_benchmarks.SimpleLPBenchmark.time_compile_problem
     15.3±0ms         15.5±0ms     1.01  simple_LP_benchmarks.SimpleFullyParametrizedLPBenchmark.time_compile_problem
      277±0ms          279±0ms     1.01  slow_pruning_1668_benchmark.SlowPruningBenchmark.time_compile_problem
      4.53±0s          4.57±0s     1.01  svm_l1_regularization.SVMWithL1Regularization.time_compile_problem
      134±0ms          135±0ms     1.01  high_dim_convex_plasticity.ConvexPlasticity.time_compile_problem
      1.00±0s          1.01±0s     1.01  finance.FactorCovarianceModel.time_compile_problem
      5.47±0s          5.48±0s     1.00  optimal_advertising.OptimalAdvertising.time_compile_problem
      4.00±0s          4.01±0s     1.00  huber_regression.HuberRegression.time_compile_problem
      336±0ms          337±0ms     1.00  gini_portfolio.Yitzhaki.time_compile_problem
      239±0ms          239±0ms     1.00  gini_portfolio.Murray.time_compile_problem
      682±0ms          681±0ms     1.00  matrix_stuffing.ConeMatrixStuffingBench.time_compile_problem
      890±0ms          888±0ms     1.00  simple_LP_benchmarks.SimpleScalarParametrizedLPBenchmark.time_compile_problem
      21.5±0s          21.4±0s     1.00  sdp_segfault_1132_benchmark.SDPSegfault1132Benchmark.time_compile_problem
     15.6±0ms         15.5±0ms     0.99  simple_QP_benchmarks.ParametrizedQPBenchmark.time_compile_problem
      2.63±0s          2.54±0s     0.96  quantum_hilbert_matrix.QuantumHilbertMatrix.time_compile_problem
      1.91±0s          1.82±0s     0.95  simple_QP_benchmarks.UnconstrainedQP.time_compile_problem