build: the libavr pin advances past phase 6

The renames land (interrupt_guard, consume_reset_cause, set_duty), the
sampler binds its input in the new converter shape (the input pack plus
in<>::start() as free-running's one kick), and the console states
.allow_baud_error = true for the 115200-at-16-MHz this board has always
spoken - the receiver-tolerance table libavr now enforces is stricter
than the rate's own +2.1 %. The loader probe reads through
avr::flash_load instead of raw pgmspace, the terminal's line buffer is
std::array with backspace and delete named, the tree is reformatted
under InsertBraces, and the sources are ASCII.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/CMakeLists.txt

@@ -1,6 +1,6 @@
 # The board has no reset line and no programming header, so the loader-entry
 # route in the emitted image is the only thing standing between a firmware change
-# and an unreflashable board. It has been wrong before — see the script.
+# and an unreflashable board. It has been wrong before - see the script.
 find_package(Python3 COMPONENTS Interpreter)
 if(Python3_FOUND)
 	add_test(NAME fantemp.reachability
@@ -8,5 +8,5 @@ if(Python3_FOUND)
 	                 --objdump ${CMAKE_OBJDUMP} --elf $<TARGET_FILE:fantemp>
 	                 --image $<TARGET_FILE_DIR:fantemp>/fantemp.bin)
 else()
-	message(STATUS "Python not found — the reachability check is skipped")
+	message(STATUS "Python not found - the reachability check is skipped")
 endif()