[roll third_party/pigweed] pw_chrono: add SystemClock::for_at_least helper

Adds a helper function for legibility to SystemClock to invoke
std::chrono::ceil for us where the return type is fixed to a
SystemClock::duration type.

Also migrates the existing uses of std::chrono::ceil to this.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/37321

third_party/pigweed Rolled-Commits: 7d254f6b7cebf88..959b883061cd100
Roller-URL: https://ci.chromium.org/b/8852914396599275072
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8852914396599275072
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I154b2a1eae45443d7a61043861e0a4e9806792c4
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/37506
Reviewed-by: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 7d254f6..959b883 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 7d254f6b7cebf8883fa314afbf4aa3f2f8afaf14
+Subproject commit 959b883061cd10018b2e69660b057e2d593cbe71