unix/main: Replace execute_from_lexer with pyexec in do_file and do_str.

Consolidates file and string execution to use the standard pyexec interface
for consistency with other ports.

Simplify execute_from_lexer for remaining usage: Remove unused LEX_SRC_VSTR
and LEX_SRC_FILENAME cases, keeping only LEX_SRC_STR for REPL and
LEX_SRC_STDIN for stdin execution.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

Author: pi-anl

ports/unix/main.c

@@ -111,8 +111,6 @@ static int handle_uncaught_exception(mp_obj_base_t *exc) {
 }
 
 #define LEX_SRC_STR (1)
-#define LEX_SRC_VSTR (2)
-#define LEX_SRC_FILENAME (3)
 #define LEX_SRC_STDIN (4)
 
 // Returns standard error codes: 0 for success, 1 for all other errors,
@@ -128,12 +126,6 @@ static int execute_from_lexer(int source_kind, const void *source, mp_parse_inpu
         if (source_kind == LEX_SRC_STR) {
             const char *line = source;
             lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, line, strlen(line), false);
-        } else if (source_kind == LEX_SRC_VSTR) {
-            const vstr_t *vstr = source;
-            lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, vstr->buf, vstr->len, false);
-        } else if (source_kind == LEX_SRC_FILENAME) {
-            const char *filename = (const char *)source;
-            lex = mp_lexer_new_from_file(qstr_from_str(filename));
         } else { // LEX_SRC_STDIN
             lex = mp_lexer_new_from_fd(MP_QSTR__lt_stdin_gt_, 0, false);
         }
@@ -251,12 +243,28 @@ static int do_repl(void) {
     #endif
 }
 
+static inline int convert_pyexec_result(int ret) {
+    // pyexec returns 1 for success, 0 for exception, PYEXEC_FORCED_EXIT for SystemExit
+    // Convert to unix port's expected codes: 0 for success, 1 for exception, FORCED_EXIT|val for SystemExit
+    if (ret == 1) {
+        return 0; // success
+    } else if (ret & PYEXEC_FORCED_EXIT) {
+        return ret; // SystemExit with exit value in lower 8 bits
+    } else {
+        return 1; // exception
+    }
+}
+
 static int do_file(const char *file) {
-    return execute_from_lexer(LEX_SRC_FILENAME, file, MP_PARSE_FILE_INPUT, false);
+    return convert_pyexec_result(pyexec_file(file));
 }
 
 static int do_str(const char *str) {
-    return execute_from_lexer(LEX_SRC_STR, str, MP_PARSE_FILE_INPUT, false);
+    vstr_t vstr;
+    vstr.buf = (char *)str;
+    vstr.len = strlen(str);
+    int ret = pyexec_vstr(&vstr, true);
+    return convert_pyexec_result(ret);
 }
 
 static void print_help(char **argv) {