[roll third_party/pigweed] pw_blob_store: Fix write limit function

- The ConservativeWriteLimit() function for blob writers was incorrectly
  implemented in the conversion to pw_stream.
- Add tests for the BlobStore read/write limit functions.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/58025

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: a514aaef53a0418..ad04bb09e6f1119
Roller-URL: https://ci.chromium.org/b/8838066303955352208
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8838066303955352208
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib09c43515f604edf96080e92f4343ec42c11f6ab
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/58027
Bot-Commit: 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 a514aae..ad04bb0 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a514aaef53a04185abb841b2877971970213b1a4
+Subproject commit ad04bb09e6f1119c5459e7ea4797de6073d2a973