drivers/serial: Modify serial/pty to allow NSH/Telnet line edit

Both the UART and PTY serial drivers previously assumed all
VT100/ANSI escape sequences were fixed 3-byte CSI sequences, causing
longer CSI and SS3 key sequences (such as Home, End, Delete, and
modified keys) to leak stray characters into the terminal when local
echo was enabled. This patch replaces the fixed-length logic with a
state machine that correctly recognizes and suppresses escape
sequences of any length, while preserving the data delivered to
applications. The change only affects local echo behavior, is fully
backward compatible, and has been validated with both interactive NSH
sessions and automated PTY tests.

Signed-off-by: Alan C. Assis <acassis@gmail.com>
Assisted-by: Claude Code

include/nuttx/serial/serial.h

@@ -326,7 +326,11 @@ struct uart_dev_s
   /* State data */
 
   uint8_t              open_count;   /* Number of times the device has been opened */
-  uint8_t              escape;       /* Number of the character to be escaped */
+  uint8_t              escape;       /* VT100/ANSI escape sequence echo-
+                                       * suppression state (see the
+                                       * UART_ESCAPE_* values used in
+                                       * uart_readv())
+                                       */
 #ifdef CONFIG_SERIAL_REMOVABLE
   volatile bool        disconnected; /* true: Removable device is not connected */
 #endif