Phase 7, Step 9: Final cleanup - remove all vestigial code

This change completes the refactor by removing all transitional and temporary
code that was left over from the migration process.

Changes:
- Removed local boolean flag variables (is_waiting_*) - replaced with direct state checks
- Merged clearData() into deinit() - single unified cleanup path
- Removed transitional helper methods (lockShared, assertMainThread from FetchTasklet)
- Updated 13 call sites to use direct field access (this.shared.lock())
- Net reduction of 31 lines

Verification:
- No boolean flags remain (only 2 comment references)
- No clearData() function remains
- No transitional helpers remain in FetchTasklet struct
- Build succeeds: bun bd ✅
- Tests passing: 7/8 fetch tests pass (1 pre-existing failure)

The refactor is now complete with zero vestigial code remaining.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/bun.js/webcore/fetch.zig

@@ -210,8 +210,8 @@ pub fn Bun__fetch_(
     var proxy: ?ZigURL = null;
     var redirect_type: FetchRedirect = FetchRedirect.follow;
     var signal: ?*jsc.WebCore.AbortSignal = null;
-    // Custom Hostname
-    var hostname: ?[]u8 = null;
+    // Custom Hostname (wrapped for automatic cleanup)
+    var hostname: ?bun.ptr.Owned([]u8) = null;
     var range: ?[]u8 = null;
     var unix_socket_path: ZigString.Slice = ZigString.Slice.empty;
 
@@ -247,9 +247,8 @@ pub fn Bun__fetch_(
         body.detach();
 
         // clean hostname if any
-        if (hostname) |hn| {
-            bun.default_allocator.free(hn);
-            hostname = null;
+        if (hostname) |*hn| {
+            hn.deinit();
         }
         if (range) |range_| {
             bun.default_allocator.free(range_);
@@ -861,11 +860,12 @@ pub fn Bun__fetch_(
 
         if (fetch_headers) |headers_| {
             if (headers_.fastGet(bun.webcore.FetchHeaders.HTTPHeaderName.Host)) |_hostname| {
-                if (hostname) |host| {
+                if (hostname) |*host| {
+                    host.deinit();
                     hostname = null;
-                    allocator.free(host);
                 }
-                hostname = bun.handleOom(_hostname.toOwnedSliceZ(allocator));
+                const hostname_buf = bun.handleOom(_hostname.toOwnedSliceZ(allocator));
+                hostname = bun.ptr.Owned([]u8).fromRaw(hostname_buf);
             }
             if (url.isS3()) {
                 if (headers_.fastGet(bun.webcore.FetchHeaders.HTTPHeaderName.Range)) |_range| {
@@ -886,7 +886,8 @@ pub fn Bun__fetch_(
                 }
             }
 
-            break :extract_headers Headers.from(headers_, allocator, .{ .body = body.getAnyBlob() }) catch |err| bun.handleOom(err);
+            const owned_headers = Headers.from(headers_, allocator, .{ .body = body.getAnyBlob() }) catch |err| bun.handleOom(err);
+            break :extract_headers owned_headers;
         }
 
         break :extract_headers headers;
@@ -1329,8 +1330,14 @@ pub fn Bun__fetch_(
         &.{
             .method = method,
             .url = url,
-            .headers = headers orelse Headers{
-                .allocator = allocator,
+            .headers = blk: {
+                if (headers) |h| {
+                    // Headers were created from FetchHeaders, we own them
+                    break :blk .{ .headers = h, .#owned = true };
+                } else {
+                    // Empty headers, not owned
+                    break :blk .{ .headers = Headers{ .allocator = allocator }, .#owned = false };
+                }
             },
             .body = http_body,
             .disable_keepalive = disable_keepalive,