docx: fix clippy large_enum_variant on main (#779)

A field's buffered result items held an InlineObject inline, which grew past
clippy's large_enum_variant limit with today's object changes. Box it.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/docx/src/read/story.rs

@@ -41,9 +41,11 @@ enum Phase {
     Result,
 }
 
+/// A buffered piece of a field's result. Objects are boxed: an inline object is much larger than
+/// a string.
 enum Item {
     Text(String),
-    Obj(InlineObject),
+    Obj(Box<InlineObject>),
 }
 
 struct FieldState {
@@ -787,7 +789,7 @@ impl Reader<'_> {
             for (it, p) in f.buf {
                 match it {
                     Item::Text(t) => self.emit_text(sc, pb, &t, &p),
-                    Item::Obj(o) => self.emit_obj(sc, pb, o, &p),
+                    Item::Obj(o) => self.emit_obj(sc, pb, *o, &p),
                 }
             }
             self.emit_obj(sc, pb, InlineObject::FieldEnd, &f.props);
@@ -828,7 +830,7 @@ impl Reader<'_> {
             for (it, p) in f.buf.drain(..) {
                 match it {
                     Item::Text(t) => pb.push_text(&t, &p),
-                    Item::Obj(o) => pb.push_obj(o, &p),
+                    Item::Obj(o) => pb.push_obj(*o, &p),
                 }
             }
         }
@@ -849,7 +851,7 @@ impl Reader<'_> {
         match sink(sc) {
             Some(f) => {
                 if f.phase == Phase::Result && f.buf.len() < 100_000 {
-                    f.buf.push((Item::Obj(o), props.clone()));
+                    f.buf.push((Item::Obj(Box::new(o)), props.clone()));
                 }
             }
             _ => pb.push_obj(o, props),