Avoid array allocation in DSL::Parameters#with

Replace `[@group, opts].compact.reduce(&:deep_merge)` with
`@group&.deep_merge(opts) || opts` to avoid allocating a temporary
array on every `with` block call.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ericproulx

lib/grape/dsl/parameters.rb

@@ -161,7 +161,7 @@ def optional(*attrs, **opts, &block)
       # @param (see #requires)
       # @option (see #requires)
       def with(**opts, &)
-        new_group_attrs = [@group, opts].compact.reduce(&:deep_merge)
+        new_group_attrs = @group&.deep_merge(opts) || opts
         new_group_scope(new_group_attrs, &)
       end