Pass ServeHeaderOptions by value instead of pointer, fine tune httplib tests (#36982)

Pass `ServeHeaderOptions` by value instead of pointer across all call
sites — no nil-check semantics are needed and the struct is small enough
that copying is fine.

## Changes

- **`services/context/base.go`**: `SetServeHeaders` and `ServeContent`
accept `ServeHeaderOptions` (value, not pointer); internal unsafe
pointer cast replaced with a clean type conversion
- **`routers/api/packages/helper/helper.go`**: `ServePackageFile`
variadic changed from `...*context.ServeHeaderOptions` to
`...context.ServeHeaderOptions`; internal variable is now a value type
- **All call sites** (13 files): `&context.ServeHeaderOptions{...}` →
`context.ServeHeaderOptions{...}`

Before/after at the definition level:
```go
// Before
func (b *Base) SetServeHeaders(opt *ServeHeaderOptions) { ... }
func (b *Base) ServeContent(r io.ReadSeeker, opts *ServeHeaderOptions) { ... }
func ServePackageFile(..., forceOpts ...*context.ServeHeaderOptions) { ... }

// After
func (b *Base) SetServeHeaders(opts ServeHeaderOptions) { ... }
func (b *Base) ServeContent(r io.ReadSeeker, opts ServeHeaderOptions) { ... }
func ServePackageFile(..., forceOpts ...context.ServeHeaderOptions) { ... }
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wxiaoguang <2114189+wxiaoguang@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/packages/helper/helper.go

@@ -39,7 +39,7 @@ func ProcessErrorForUser(ctx *context.Context, status int, errObj any) string {
 
 // ServePackageFile the content of the package file
 // If the url is set it will redirect the request, otherwise the content is copied to the response.
-func ServePackageFile(ctx *context.Context, s io.ReadSeekCloser, u *url.URL, pf *packages_model.PackageFile, forceOpts ...*context.ServeHeaderOptions) {
+func ServePackageFile(ctx *context.Context, s io.ReadSeekCloser, u *url.URL, pf *packages_model.PackageFile, forceOpts ...context.ServeHeaderOptions) {
 	if u != nil {
 		ctx.Redirect(u.String())
 		return
@@ -47,11 +47,11 @@ func ServePackageFile(ctx *context.Context, s io.ReadSeekCloser, u *url.URL, pf
 
 	defer s.Close()
 
-	var opts *context.ServeHeaderOptions
+	var opts context.ServeHeaderOptions
 	if len(forceOpts) > 0 {
 		opts = forceOpts[0]
 	} else {
-		opts = &context.ServeHeaderOptions{
+		opts = context.ServeHeaderOptions{
 			Filename:     pf.Name,
 			LastModified: pf.CreatedUnix.AsLocalTime(),
 		}