refactor(fetcher): drop the Android DownloadManager fallback

[msluszniak]

Description

react-native-blob-util 0.24.11 fixed the Android in-process reader that stopped after 8 KB (#475), which was the only reason Android had a download backend of its own. Both platforms now share the streaming fallback, leaving one mechanism (the optional background downloader) plus one shared fallback.

• peer range ^0.24.0 -> >=0.24.11; apps and the lib devDependency move to ^0.25.0
• removes downloadUrlViaAndroidDownloadManager and the IS_ANDROID backend branch
• removes reassemble32BitCounter; the 32-bit progress overflow came from DownloadManager's cursor column being read with getInt, and the in-process path reports bytes as real numbers
• the Android cache directory stays where it is, since moving it would orphan every model already downloaded

Introduces a breaking change?

• Yes
• No

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Documentation update (improves or adds clarity to existing documentation)
• Other (chores, tests, code style improvements etc.)

Tested on

• iOS
• Android

Testing instructions

1. Run apps/nlp on an Android device without @kesha-antonov/react-native-background-downloader installed.
2. Download a model larger than 2 GB, e.g. llama_3_2_3b_xnnpack_spinquant.pte.
3. Progress should climb monotonically to 100% and the cached file should match the server's length.

Screenshots

Related issues

Closes #1401

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes generate no new warnings

Additional notes

Verified on a Galaxy S26 Ultra: 2,553,367,552 bytes downloaded in 146 s, matching the server's x-linked-size exactly. This is the first time the >2 GB path has run end to end, since it has been broken since it landed.

Without the optional background downloader, Android downloads no longer continue while the app is suspended; they resume on the next download call, as on iOS.