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.

Also fixes #741, so this does not break correct code: the raw snapshot
hooks resolve to a DocumentSnapshot/QuerySnapshot, so their options are
now typed with the hook's own resolved type rather than the unwrapped
data type. Without that, seeding them with a snapshot (the only value a
caller can actually have) stopped compiling.

Adds `src/reactfire-options.type-test.ts`, type-level assertions riding
the existing `tsc --noEmit` CI and kept out of the tarball by
`.npmignore`. Both directions are covered: a snapshot hook refuses raw
data, a data hook refuses a snapshot. Mutation-verified, reverting either
fix fails them.

No runtime change.

Fixes #383. Fixes #741.

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