Refactor token mapping: use keyword map for tokenization instead of strcmp

- Created KeywordMap structure with keyword-to-token mapping at top of token.c
- Added lookup_keyword() function to check if identifier is a keyword
- Replaced 3 strcmp calls (lines 99-101) with single lookup_keyword() call
- Removed token_to_string() function and its tests (3 tests removed)
- Single easy-to-read and modify keyword map serves both documentation and implementation
- Added new keywords by editing the keywords[] array at top of token.c

All 12 tests passing (removed token_to_string tests which are now unnecessary).

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

v0/token.c

@@ -5,41 +5,40 @@
 #include <string.h>
 
 /**
- * Easy-to-read and modify token-to-string mapping.
- * Order must match the Token enum in token.h.
+ * Easy-to-read and modify keyword-to-token mapping.
+ * Add new keywords here.
  */
-static const char* token_names[] = {
-	"module",
-	"import",
-	"semicolon",
-	"paren_open",
-	"paren_close",
-	"bracket_open",
-	"bracket_close",
-	"comma",
-	"void",
-	"identifier",
+typedef struct {
+	const char* keyword;
+	Token token;
+} KeywordMap;
+
+static const KeywordMap keywords[] = {
+	{"module", TOKEN_MODULE},
+	{"import", TOKEN_IMPORT},
+	{"void", TOKEN_VOID},
 };
 
+/**
+ * Look up a keyword in the keyword map.
+ * Returns TOKEN_IDENTIFIER if not found.
+ */
+static Token lookup_keyword(const char* str) {
+	int count = sizeof(keywords) / sizeof(keywords[0]);
+	for (int i = 0; i < count; i++) {
+		if (strcmp(keywords[i].keyword, str) == 0) {
+			return keywords[i].token;
+		}
+	}
+	return TOKEN_IDENTIFIER;
+}
+
 struct TokenStream {
 	Buffer* buffer;
 	char lookahead;
 	int has_lookahead;
 };
 
-/**
- * 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) {
-	int count = sizeof(token_names) / sizeof(token_names[0]);
-	if (token >= 0 && token < count) {
-		return token_names[token];
-	}
-	return "unknown";
-}
-
 /**
  * Check if a character is the start of an identifier.
  */
@@ -96,11 +95,7 @@ static Token read_keyword_or_identifier(TokenStream* ts, char first) {
 	buffer[index] = '\0';
 
 	/* Check for keywords */
-	if (strcmp(buffer, "module") == 0) return TOKEN_MODULE;
-	if (strcmp(buffer, "import") == 0) return TOKEN_IMPORT;
-	if (strcmp(buffer, "void") == 0) return TOKEN_VOID;
-
-	return TOKEN_IDENTIFIER;
+	return lookup_keyword(buffer);
 }
 
 TokenStream* tokenstream_open(Buffer* buffer) {