timeline: refactor tabs into TimelineView

TimelineView is a filtered view of a timeline. We will use this for
future tab rendering. We also introduce a new "selection" concept for
selecting notes on different timeline views. This is in preparation for
vim keybindings.

src/notecache.rs

@@ -1,15 +1,21 @@
 use crate::time::time_ago_since;
 use crate::timecache::TimeCached;
-use nostrdb::{Note, NoteReply, NoteReplyBuf};
+use nostrdb::{Note, NoteKey, NoteReply, NoteReplyBuf};
+use std::collections::HashMap;
 use std::time::Duration;
 
+#[derive(Default)]
 pub struct NoteCache {
+    pub cache: HashMap<NoteKey, CachedNote>,
+}
+
+pub struct CachedNote {
     reltime: TimeCached<String>,
     pub reply: NoteReplyBuf,
     pub bar_open: bool,
 }
 
-impl NoteCache {
+impl CachedNote {
     pub fn new(note: &Note<'_>) -> Self {
         let created_at = note.created_at();
         let reltime = TimeCached::new(
@@ -18,7 +24,7 @@ impl NoteCache {
         );
         let reply = NoteReply::new(note.tags()).to_owned();
         let bar_open = false;
-        NoteCache {
+        CachedNote {
             reltime,
             reply,
             bar_open,