feat: add support for escaped characters in RegexParser and corresponding tests

lib/src/main/kotlin/org/example/Parser.kt

@@ -8,11 +8,15 @@ import com.github.h0tk3y.betterParse.lexer.regexToken
 import com.github.h0tk3y.betterParse.parser.Parser
 
 class RegexParser : Grammar<RegexItem>() {
+  // val bracketContent by regexToken("[^\\]]*")
+  val escapedCharacter by regexToken("\\\\[+*?.()|\\[\\]]")
   val postfixOperator by regexToken("[+*?]")
   val alternationSymbol by literalToken("|")
   val openParenSymbol by literalToken("(")
   val closeParenSymbol by literalToken(")")
-
+  val bracketOpen by literalToken("[")
+  val bracketClose by literalToken("]")
+  
   val dot by literalToken(".")
   val charToken by regexToken("[a-zA-Z0-9]")
 
@@ -21,6 +25,7 @@ class RegexParser : Grammar<RegexItem>() {
   val item: Parser<RegexItem> by
           char or
                   (dot asJust DotItem()) or
+                  (escapedCharacter map { CharItem(it.text.substring(1)) }) or
                   (skip(openParenSymbol) and (parser(::rootParser)) and skip(closeParenSymbol))
 
   val term: Parser<RegexItem> by

lib/src/main/kotlin/org/example/RegexItem.kt

@@ -66,7 +66,21 @@ class AndThenItem(val left: RegexItem, val right: RegexItem) : RegexItem {
 }
 
 class CharItem(val value: String) : RegexItem {
-  override fun toString(): String = value
+  override fun toString(): String = 
+    // escape 특수 문자를 처리하여 출력
+    when (value) {
+      "+" -> "\\+"
+      "*" -> "\\*"
+      "?" -> "\\?"
+      "." -> "\\."
+      "(" -> "\\("
+      ")" -> "\\)"
+      "|" -> "\\|"
+      "[" -> "\\["
+      "]" -> "\\]"
+      else -> value // 일반 문자 그대로 반환
+    }
+  
   override fun findMatch(str: String): AvailableState {
     return when {
       // 첫번째 문자가 value와 일치하는지 확인

lib/src/test/kotlin/org/example/ParserTest.kt

@@ -107,4 +107,13 @@ class ParserTest {
         assert(result.match("ba").isSuccess)
         assert(result.match("bca").isSuccess)
     }
+    @Test
+    fun testEscapedCharacter() {
+        val input = "\\+"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("\\+", result.toString())
+        assert(result.match("+").isSuccess)
+        assert(!result.match("a").isSuccess)
+    }
 }