Implement token.c with comprehensive tests and easy-to-modify token mapping

- Created token-to-string mapping array parallel to Token enum in token.c
- Implemented TokenStream with lookahead buffering for proper tokenization
- Implemented tokenstream_open/close/next functions with support for:
  - Keywords (module, import, void)
  - Symbols (parentheses, brackets, comma, semicolon)
  - Identifiers (alphanumeric starting with letter or underscore)
  - Comment skipping (// style)
  - Whitespace handling
- Added token_to_string function to token.h for token inspection
- Created comprehensive test suite (15 tests) covering all token types and edge cases
- All tests pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

v0/token.h

@@ -26,6 +26,13 @@ typedef enum {
 
 typedef struct TokenStream TokenStream;
 
+/**
+ * Convert a Token enum to its string representation.
+ * @param token The token to convert.
+ * @returns The string name of the token.
+ */
+const char* token_to_string(Token token);
+
 /**
  * Opens a file and returns a TokenStream for it.
  * @param path The path to the file.