[roll third_party/pigweed] pw_rpc: Python client support for keeping RPCs open

- Support opening an RPC without calling it in the core pw_rpc client.
- Provide a keep_open option so the client keep RPCs going even if they
  are completed.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/39823

third_party/pigweed Rolled-Commits: 2981da2fbef7b80..e0ae9b10b87a9d0
Roller-URL: https://ci.chromium.org/b/8850676915456518336
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8850676915456518336
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I1ae510837d11e47ac0af44606256188c7550d094
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/40045
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 2981da2..e0ae9b1 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 2981da2fbef7b80366a0c7d7931b651cb0c9198c
+Subproject commit e0ae9b10b87a9d078c6eb18b76375864fdaab636