Update benchmarks for MPM move

Author: chahak13

benchmarks/2d/uniaxial_nodal_forces/test_benchmark.py

@@ -1,7 +1,7 @@
 import os
 from pathlib import Path
 import jax.numpy as jnp
-from diffmpm.solver import MPM
+from diffmpm import MPM
 
 curr_filepath = Path(__file__).absolute()
 curr_dir = curr_filepath.parent

benchmarks/2d/uniaxial_particle_traction/test_benchmark.py

@@ -1,7 +1,7 @@
 import os
 from pathlib import Path
 import jax.numpy as jnp
-from diffmpm.solver import MPM
+from diffmpm import MPM
 
 curr_filepath = Path(__file__).absolute()
 curr_dir = curr_filepath.parent

benchmarks/2d/uniaxial_stress/test_benchmark.py

@@ -1,7 +1,7 @@
 import os
 from pathlib import Path
 import jax.numpy as jnp
-from diffmpm.solver import MPM
+from diffmpm import MPM
 
 curr_filepath = Path(__file__).absolute()
 curr_dir = curr_filepath.parent