Make sure (most) queries avoid table scans.

I've exempted inserts (they never scan in the first place), queries on `event_sequence` (at most one row), and the coalesce()s used for event replay (for now; these are obviously a performance risk area and need addressing).

Method:

```
find .sqlx -name 'query-*.json' -exec jq -r '"explain query plan " + .query + ";"' {} + > explain.sql
```

Then go query by query through the resulting file.

1 files changed, 0 insertions, 62 deletions

diff --git a/.sqlx/query-40e0310af2814435cca882701b86eddb5a1114202ba385f66f131b1601feec11.json b/.sqlx/query-40e0310af2814435cca882701b86eddb5a1114202ba385f66f131b1601feec11.json
deleted file mode 100644
index 3147d7f..0000000
--- a/.sqlx/query-40e0310af2814435cca882701b86eddb5a1114202ba385f66f131b1601feec11.json
+++ /dev/null
@@ -1,62 +0,0 @@
-{
-  "db_name": "SQLite",
-  "query": "\n                select\n                    message.channel as \"channel: channel::Id\",\n                    message.sender as \"sender: login::Id\",\n                    id as \"id: Id\",\n                    message.body as \"body: Body\",\n                    message.sent_at as \"sent_at: DateTime\",\n                    message.sent_sequence as \"sent_sequence: Sequence\",\n                    deleted.deleted_at as \"deleted_at: DateTime\",\n                    deleted.deleted_sequence as \"deleted_sequence: Sequence\"\n                from message\n                left join message_deleted as deleted\n                    using (id)\n                where message.channel = $1\n                    and deleted.id is null\n            ",
-  "describe": {
-    "columns": [
-      {
-        "name": "channel: channel::Id",
-        "ordinal": 0,
-        "type_info": "Text"
-      },
-      {
-        "name": "sender: login::Id",
-        "ordinal": 1,
-        "type_info": "Text"
-      },
-      {
-        "name": "id: Id",
-        "ordinal": 2,
-        "type_info": "Text"
-      },
-      {
-        "name": "body: Body",
-        "ordinal": 3,
-        "type_info": "Text"
-      },
-      {
-        "name": "sent_at: DateTime",
-        "ordinal": 4,
-        "type_info": "Text"
-      },
-      {
-        "name": "sent_sequence: Sequence",
-        "ordinal": 5,
-        "type_info": "Integer"
-      },
-      {
-        "name": "deleted_at: DateTime",
-        "ordinal": 6,
-        "type_info": "Text"
-      },
-      {
-        "name": "deleted_sequence: Sequence",
-        "ordinal": 7,
-        "type_info": "Integer"
-      }
-    ],
-    "parameters": {
-      "Right": 1
-    },
-    "nullable": [
-      false,
-      false,
-      false,
-      true,
-      false,
-      false,
-      true,
-      true
-    ]
-  },
-  "hash": "40e0310af2814435cca882701b86eddb5a1114202ba385f66f131b1601feec11"
-}