fix: tighten ReactFireOptions generic types, remove T | any widening

Removes `| any` from `initialData` and `startWithValue`, so a value of the
wrong type is a TypeScript error rather than silently accepted. `T | any`
collapses to `any`, so the generic never enforced anything.

Tightens `checkIdField` to read `options?.idField` directly, and narrows
`checkOptions` / `checkinitialData` from `any` to `unknown`. Both are kept
as exports; removal is tracked in #754.

Adds casts at the rxfire `docData` / `collectionData` call sites, where
rxfire expects `keyof T` and the field is a plain string.

Adds `src/reactfire-options.type-test.ts`, five `@ts-expect-error`
assertions riding the existing `tsc --noEmit` CI, kept out of the tarball
by `.npmignore`. The negative-case consts are consumed so the directives
are load-bearing: without that, `noUnusedLocals` satisfies them with a
TS6133 and the file passes even if the tightening is reverted.

Breaking for the raw snapshot hooks: their correct `initialData` is a
`DocumentSnapshot<T>` / `QuerySnapshot<T>`, and the interface now says
`T`, so correct usage stops compiling. #741 tracks the real fix and is
required for 5.0.0.

Fixes #383.

Author: tyler-reitz

.npmignore

@@ -0,0 +1 @@
+src/*.type-test.ts

README.md

@@ -13,7 +13,7 @@ Firebase.
 
 ## Platform support
 
-ReactFire is designed for **web React apps** and wraps the [Firebase Web SDK](https://firebase.google.com/docs/web/setup). It is not compatible with React Native or Expo. For React Native projects, use [react-native-firebase](https://rnfirebase.io/) instead.
+ReactFire is designed for **web React apps** and wraps the [Firebase JavaScript SDK](https://firebase.google.com/docs/web/setup). It is not compatible with React Native or Expo. For React Native projects, use [react-native-firebase](https://rnfirebase.io/) instead.
 
 ## Install