Clone response in Lookup Race Response algorithm (#1811)

The "Lookup Race Response" algorithm returned a response from the race
response map directly. This could lead to issues where a response body
is consumed more than once, as a Response object's body cannot be reused
across multiple fetch operations.

This change modifies the algorithm to return a clone of the response,
aligning with the Fetch specification's standard practice for handling
responses that may be used by multiple consumers. This ensures that each
fetch handler receives a distinct, readable stream.

See also: https://fetch.spec.whatwg.org/#concept-response-clone

Author: yoshisatoyanagisawa

index.bs

@@ -4158,7 +4158,7 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
       1. If |map|[|request|] [=map/exists=], then:
         1. Let |entry| be |map|[|request|].
         1. Wait until |entry|'s [=race response/value=] is not "<code>pending</code>"
-        1. If |entry|'s [=race response/value=] is [=/response=], return |entry|'s [=race response/value=].
+        1. If |entry|'s [=race response/value=] is a [=/response=], return the result of <a for="response">cloning</a> |entry|'s [=race response/value=].
       1. Return null.
   </section>
 </section>