pw_transfer: Add hdlc escape integration test
pw_transfer: Add hdlc escape integration test

Adds a test that fills and 8K buffer with 0x7e which is the
HLDC escape sequence.

Change-Id: I043aab2f52428cf403b7f2be308a33fa0eb836e0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/87740
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Pigweed-Auto-Submit: Erik Gilling <1100d3bbb092e6691a138903fe8ea324306d03ea@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed