Update NPM packaging, linting, and a bunch of types (#275)

Preparation for
https://github.com/webrecorder/archiveweb.page/issues/198 /
https://github.com/webrecorder/archiveweb.page/pull/199.

## Changes

- Organizes published files more cleanly, using `dist/types` folder as
the target for type declarations and sourcemaps
- Configures type field in `package.json`
- Updates ESLint & its config
  - Sets up type-informed linting rules mirroring browsertrix
- Adds a bunch of other useful eslint and eslint-typescript rules, and
applies auto-fixes to the codebase
- Cleans up a bunch of types throughout the codebase, particularly parts
of the code used by ArchiveWebPage
- Changes `ItemIndex#_deleting` from `private` to `protected` so that a
part of AWP that extends it can do so properly
- Makes a bunch of previously-implied [non-null
assertions](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#non-null-assertion-operator-postfix-)
explicit
- Updates `URLResource` and `ItemType` types (and renames `Item` →
`ItemType` to disambiguate from the `Item` class)
- Removes `node-sass` and replaces it with `sass-embedded` for much
quicker installs and compilation

src/types.ts

@@ -1,4 +1,21 @@
-export interface Item {
+export type URLResource = {
+  id: number;
+  title: string;
+  url: string;
+  mime: string;
+  status: string;
+  date: Date;
+  ts: string;
+  desc?: string;
+  timestamp?: string;
+  size: number;
+  favIconUrl: string;
+  text?: string;
+};
+
+export type Page = URLResource;
+
+export type ItemType = {
   filename: string;
   sourceUrl: string;
   replayPrefix: string;
@@ -26,11 +43,10 @@ export interface Item {
     software?: string;
   };
   onDemand?: boolean;
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO fixme
-  pages?: any[];
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO fixme
-  lists?: any[];
+  pages: URLResource[];
+  curatedPages: (URLResource & { list: string })[];
+  lists: URLResource[];
   ctime?: string;
   totalSize?: unknown;
   size?: number | string;
-}
+};