Update changeset for libxmtp v1.6.1

Includes updates to `libxmtp` with new features and enhancements.

Author: neekolas

.changeset/fluffy-balloons-search.md

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+---
+"@fake-scope/fake-pkg": patch
+---
+
+Updates to `libxmtp` v1.6.1 which includes many features and enhancements
+
+https://github.com/xmtp/libxmtp/releases/tag/v1.6.1