Support custom `boxer_header: str` provided by `pformat_boxed_tb()` caller

tractor/devx/pformat.py

@@ -53,6 +53,7 @@ def pformat_boxed_tb(
 
     tb_box_indent: int|None = None,
     tb_body_indent: int = 1,
+    boxer_header: str = '-'
 
 ) -> str:
     '''
@@ -88,9 +89,9 @@ def pformat_boxed_tb(
 
     tb_box: str = (
         f'|\n'
-        f' ------ - ------\n'
+        f' ------ {boxer_header} ------\n'
         f'{tb_body}'
-        f' ------ - ------\n'
+        f' ------ {boxer_header}- ------\n'
         f'_|\n'
     )
     tb_box_indent: str = (