[roll] Roll fuchsia [roll] Roll third_party/pigweed pw_rpc: Use local encoding buffers when dynamic allocation is enabled

There's no need to use the global encoding buffer if we are dynamically
allocating anyways. This will unblock future improvements to let
Channel::Send happen without holding global lock.

Identical reland as it turns out the perf issues were due to the rename
of the encoding buffer causing it to be placed in slow memory on some
downstream devices.

Original-Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/406812
Original-Original-Revision: 81bfe9c52564e673bef6f74177fa032b11a845d3

Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1613066
Original-Original-Revision: 43e39b7f96a496c195345e8ee579cf25257ed676
GitOrigin-RevId: bd2654c6ff520c16823b10ca74cb6c5b67b453fc
Change-Id: I2d3cf63887a979a1289180d61c92f0c1a36cfa37
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1614029
Cr-Commit-Position: refs/heads/main@{#192802}
diff --git a/stem b/stem
index 3479c4e..4f550d3 100644
--- a/stem
+++ b/stem
@@ -8,6 +8,6 @@
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