fix(#136): add neverForLocation option to expo plugin

[q-bird]

Fixes #136.

Adds a neverForLocation prop to the Expo config plugin, so Expo apps can reach the native path added in #135 without writing their own manifest mod.

• neverForLocation: false (default) - no change to the generated manifest.
• neverForLocation: true - BLUETOOTH_SCAN is declared with android:usesPermissionFlags="neverForLocation".
• neverForLocation: true and transport: "ble" - ACCESS_FINE_LOCATION is also capped at maxSdkVersion="30". It stays uncapped when SoftAP is in play, since Wi-Fi scanning does require location.

Also makes addPermission merge attributes onto an existing entry instead of returning early. It was add-only, so if another plugin declared BLUETOOTH_SCAN first (react-native-ble-plx does) the flag would silently never land, depending on plugin order in app.json. It only writes attributes it was asked to write.

README updated with the new prop. Verified against a real expo prebuild output for the ble/softap/both x neverForLocation matrix, not just unit-level logic.

[mateogianolio]

Fantastic! 💯