appease clippy

```
error: large size difference between variants
   --> crates/notedeck_columns/src/column.rs:249:1
    |
249 | / pub enum IntermediaryRoute {
250 | |     Timeline(Timeline),
    | |     ------------------ the largest variant contains at least 280 bytes
251 | |     Route(Route),
    | |     ------------ the second-largest variant contains at least 72 bytes
252 | | }
    | |_^ the entire enum is at least 280 bytes
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
    = note: `-D clippy::large-enum-variant` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::large_enum_variant)]`
help: consider boxing the large fields to reduce the total size of the enum
    |
250 -     Timeline(Timeline),
250 +     Timeline(Box<Timeline>),
    |

error: could not compile `notedeck_columns` (lib) due to 1 previous error
```

Signed-off-by: kernelkind <kernelkind@gmail.com>

crates/notedeck_columns/src/column.rs

@@ -124,7 +124,7 @@ impl Columns {
                 IntermediaryRoute::Timeline(mut timeline) => {
                     let route = Route::timeline(timeline.kind.clone());
                     timeline.subscription.increment();
-                    timeline_cache.insert(timeline.kind.clone(), timeline);
+                    timeline_cache.insert(timeline.kind.clone(), *timeline);
                     route
                 }
                 IntermediaryRoute::Route(route) => route,
@@ -247,7 +247,7 @@ impl Columns {
 }
 
 pub enum IntermediaryRoute {
-    Timeline(Timeline),
+    Timeline(Box<Timeline>),
     Route(Route),
 }
 

crates/notedeck_columns/src/storage/decks.rs

@@ -351,9 +351,9 @@ impl CleanIntermediaryRoute {
         match self {
             CleanIntermediaryRoute::ToTimeline(timeline_kind) => {
                 let txn = Transaction::new(ndb).unwrap();
-                Some(IntermediaryRoute::Timeline(
+                Some(IntermediaryRoute::Timeline(Box::new(
                     timeline_kind.into_timeline(&txn, ndb)?,
-                ))
+                )))
             }
             CleanIntermediaryRoute::ToRoute(route) => Some(IntermediaryRoute::Route(route)),
         }