[ruby/json] 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 https://github.com/ruby/json/commit/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
```

https://github.com/ruby/json/commit/b8cdf3282d

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

1 files changed, 0 insertions, 25 deletions

diff --git a/ext/json/parser/parser.c b/ext/json/parser/parser.c
index d9b578f245..68ff6d7ac3 100644
--- a/ext/json/parser/parser.c
+++ b/ext/json/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);