[roll third_party/pigweed] pw_perf_test: Refactor event handler types

This CL refactors the `EventHandler` to achieve two things:
 - It uses more pw_metric-friendly floats over int64_ts.
 - It separates logging the metrics to a `TestCaseMeasure` method to
   allow handling multiple measurements.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/179611

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 9ea4f88a8b21a90..2e5c85c3f8a88ea
Roller-URL: https://ci.chromium.org/b/8761696777789225521
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I7cb71454223c1fcb78a1a983f6829fe94f3398a9
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/185133
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.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 9ea4f88..2e5c85c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 9ea4f88a8b21a909b41462b2420bbbe8bfa97187
+Subproject commit 2e5c85c3f8a88ead6ec596fcc58c11a33d43d155