pw_watch: Support mypy --no-implicit-optional
pw_watch: Support mypy --no-implicit-optional

Change-Id: Ic250ed3810a91075c9a0ef6ca5bdd55d9dd4ac0b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/115082
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Pigweed-Auto-Submit: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>

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