roll: third_party/pigweed: docs/style: Require unit tests to be in unnamed namespace

- Mention in the style guide that unit tests must be declared in an
  unnamed namespace to avoid linking issues.
- Add unnamed namespaces to tests that are missing them.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/231211

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 972e2d48d807a8e..b816ed566711b10
Roller-URL: https://ci.chromium.org/b/8738955140397257713
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ifdfa1e743bfcc0f1797138db2a7319e3239bbfd1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/231274
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 972e2d4..b816ed5 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 972e2d48d807a8eb7d97767ef9afc3f55890ccee
+Subproject commit b816ed566711b10544fc1ae2d5154e077737522c