[roll third_party/pigweed] pw_rpc: Easier callback_client RPC invocations

- Accept request proto arguments directly in callback-based RPC
  invocations through the request_args argument.
- Provide the request and response types directly on the method client
  as request and response.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/55502

third_party/pigweed Rolled-Commits: 6ef8a1d50a0ab2d..af7f5ef93da4372
Roller-URL: https://ci.chromium.org/b/8839790416171594240
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8839790416171594240
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I4c001f742c087c186ca6229e73ed7499a14dcad1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/56126
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 6ef8a1d..af7f5ef 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 6ef8a1d50a0ab2d97fafcb51d49906b813d59ec1
+Subproject commit af7f5ef93da43726f9dce144f1209a0c2b800c02