refactor: FORMAT_SEPARATOR: Change to a rarer delimeter (#475)

Fixes #471, #472

Author: tony

CHANGES

@@ -14,6 +14,13 @@ $ pip install --user --upgrade --pre libtmux
 
 <!-- Maintainers and contributors: Insert change notes for the next release above -->
 
+### Breaking internal change
+
+- Default format separator (`LIBTMUX_TMUX_FORMAT_SEPARATOR`): `|` -> `␞` (#475,
+  in re: #471, #472)
+
+  Fixes `buffer_sample` with pipes causing `fetch_objs()`-powered listings to fail unexpectedly.
+
 ## libtmux 0.20.0 (2023-01-15)
 
 ### What's new

src/libtmux/formats.py

@@ -8,7 +8,7 @@
 """
 import os
 
-FORMAT_SEPARATOR = os.environ.get("LIBTMUX_TMUX_FORMAT_SEPARATOR", "|")
+FORMAT_SEPARATOR = os.environ.get("LIBTMUX_TMUX_FORMAT_SEPARATOR", "␞")
 
 SESSION_FORMATS = [
     "session_name",