pw_unit_test: Add py_proto_library target
pw_unit_test: Add py_proto_library target

Bug: b/240474950
Change-Id: I5aaa5336dd78bd18a06e6709a2ffd4ce54e2dc0e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/106915
Reviewed-by: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>
Pigweed-Auto-Submit: Ted Pudlik <c7372cc3e451acc046049fca9e050bcb2a4a3d11@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed