[fetch] Fix sporadic data corruption bug in HTTP client and add fast path

- This removes memory pooling from the HTTP client which sometimes caused invalid memory to be written to the response body.
- This adds a fast path for small HTTP/HTTPS responses that makes it a single memory allocation for the response body, instead of copying & allocating a temporary buffer

cc @Electroid

src/bun.js/javascript.zig

@@ -436,10 +436,10 @@ pub const VirtualMachine = struct {
     modules: ModuleLoader.AsyncModule.Queue = .{},
     aggressive_garbage_collection: GCLevel = GCLevel.none,
 
-    pub const GCLevel = enum {
-        none,
-        mild,
-        aggressive,
+    pub const GCLevel = enum(u3) {
+        none = 0,
+        mild = 1,
+        aggressive = 2,
     };
 
     pub threadlocal var is_main_thread_vm: bool = false;