feat(lex_parser): rename functions and update header guard prefix

- Change header guard from `__SMCC_LEX_PARSER_H__` to `__SCC_LEX_PARSER_H__`
- Prefix all lexer functions with `scc_` (e.g., `lex_parse_char` → `scc_lex_parse_char`)
- Add new helper function `scc_lex_parse_is_identifier_header`
- Update references in source and test files to use new function names
- Replace `core_stream_eof` with `scc_stream_eof` for consistency

libs/lex_parser/tests/test_char.c

@@ -8,7 +8,7 @@ cbool check_char(const char *str, int expect, int *output) {
     scc_mem_probe_stream_t mem_stream;
     scc_probe_stream_t *stream =
         scc_mem_probe_stream_init(&mem_stream, str, scc_strlen(str), false);
-    *output = lex_parse_char(stream, &pos);
+    *output = scc_lex_parse_char(stream, &pos);
     return *output == expect;
 }
 
@@ -22,8 +22,8 @@ cbool check_char(const char *str, int expect, int *output) {
 #define CHECK_CHAR_INVALID(str)                                                \
     do {                                                                       \
         int _output;                                                           \
-        check_char(str, core_stream_eof, &_output);                            \
-        TEST_CHECK(_output == core_stream_eof);                                \
+        check_char(str, scc_stream_eof, &_output);                             \
+        TEST_CHECK(_output == scc_stream_eof);                                 \
     } while (0)
 
 void test_simple_char(void) {