Split physics.py out into a separate py_library

Much easier to change dependencies.

Change-Id: I03d3988bb70fa0060b64b4e6af7e76344034529f
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/frc971/control_loops/swerve/velocity_controller/BUILD b/frc971/control_loops/swerve/velocity_controller/BUILD
index f0e199b..7d376bd 100644
--- a/frc971/control_loops/swerve/velocity_controller/BUILD
+++ b/frc971/control_loops/swerve/velocity_controller/BUILD
@@ -28,11 +28,11 @@
     srcs = [
         "main.py",
         "model.py",
-        "physics.py",
         "train.py",
     ],
     deps = [
         ":experience_buffer",
+        ":physics",
         "//frc971/control_loops/swerve:jax_dynamics",
         "@pip//absl_py",
         "@pip//aim",
@@ -47,15 +47,26 @@
     ],
 )
 
+py_library(
+    name = "physics",
+    srcs = ["physics.py"],
+    deps = [
+        "//frc971/control_loops/swerve:jax_dynamics",
+        "@pip//flax",
+        "@pip//jax",
+        "@pip//jaxtyping",
+    ],
+)
+
 py_binary(
     name = "lqr_plot",
     srcs = [
         "lqr_plot.py",
         "model.py",
-        "physics.py",
     ],
     deps = [
         ":experience_buffer",
+        ":physics",
         "//frc971/control_loops/swerve:jax_dynamics",
         "@pip//absl_py",
         "@pip//flashbax",