parser.c: Skip checking for escape sequences in rstring_cache_fetch

The caller already know if the string contains escape sequences
so this check is redundant.

Also stop calling `rstring_cache_fetch` from `json_string_unescape`
as we know it won't match anyways.

```
== Parsing twitter.json (567916 bytes)
ruby 3.4.6 (2025-09-16 revision dbd83256b1) +YJIT +PRISM [arm64-darwin24]
Warming up --------------------------------------
               after   122.000 i/100ms
Calculating -------------------------------------
               after      1.226k (± 0.3%) i/s  (815.85 μs/i) -      6.222k in   5.076282s

Comparison:
              before:     1206.2 i/s
               after:     1225.7 i/s - 1.02x  faster
```

Co-Authored-By: Scott Myron <samyron@gmail.com>

Author: byroot

ext/json/ext/parser/parser.c

@@ -122,12 +122,6 @@ static VALUE rstring_cache_fetch(rvalue_cache *cache, const char *str, const lon
         }
     }
 
-    if (RB_UNLIKELY(memchr(str, '\\', length))) {
-        // We assume the overwhelming majority of names don't need to be escaped.
-        // But if they do, we have to fallback to the slow path.
-        return Qfalse;
-    }
-
     VALUE rstring = build_interned_string(str, length);
 
     if (cache->length < JSON_RVALUE_CACHE_CAPA) {
@@ -174,12 +168,6 @@ static VALUE rsymbol_cache_fetch(rvalue_cache *cache, const char *str, const lon
         }
     }
 
-    if (RB_UNLIKELY(memchr(str, '\\', length))) {
-        // We assume the overwhelming majority of names don't need to be escaped.
-        // But if they do, we have to fallback to the slow path.
-        return Qfalse;
-    }
-
     VALUE rsymbol = build_symbol(str, length);
 
     if (cache->length < JSON_RVALUE_CACHE_CAPA) {
@@ -652,19 +640,6 @@ static VALUE json_string_unescape(JSON_ParserState *state, const char *string, c
     int unescape_len;
     char buf[4];
 
-    if (is_name && state->in_array) {
-        VALUE cached_key;
-        if (RB_UNLIKELY(symbolize)) {
-            cached_key = rsymbol_cache_fetch(&state->name_cache, string, bufferSize);
-        } else {
-            cached_key = rstring_cache_fetch(&state->name_cache, string, bufferSize);
-        }
-
-        if (RB_LIKELY(cached_key)) {
-            return cached_key;
-        }
-    }
-
     VALUE result = rb_str_buf_new(bufferSize);
     rb_enc_associate_index(result, utf8_encindex);
     buffer = RSTRING_PTR(result);

test/json/json_parser_test.rb

@@ -344,6 +344,18 @@ def test_parse_big_integers
     assert_equal orig, parse(json5)
   end
 
+  def test_parse_escaped_key
+    doc = {
+      "test\r1" => 1,
+      "entries" => [
+        "test\t2" => 2,
+        "test\n3" => 3,
+      ]
+    }
+
+    assert_equal doc, parse(JSON.generate(doc))
+  end
+
   def test_parse_duplicate_key
     expected = {"a" => 2}
     expected_sym = {a: 2}