stm32/usart: expose all functionality as inherent methods.

tests/stm32/teleprobe.sh

@@ -0,0 +1,12 @@
+echo Running target=$1 elf=$2
+STATUSCODE=$(
+    curl \
+        -sS \
+        --output /dev/stderr \
+        --write-out "%{http_code}" \
+        -H "Authorization: Bearer $TELEPROBE_TOKEN" \
+        https://teleprobe.embassy.dev/targets/$1/run --data-binary @$2
+)
+echo
+echo HTTP Status code: $STATUSCODE
+test "$STATUSCODE" -eq 200