Fix InputStream leak in UploadModel.buildContributions()

[Roniscend]

Description (required)
Wrapped the InputStream initialization in a Kotlin .use block to guarantee safe resource closure
Fixes #6853

Tests performed (required)

Tested 6.5.0-debug on Pixel 9(Android 16)

[Copilot]

Pull request overview

This PR addresses Issue #6853 by ensuring the InputStream opened in UploadModel.buildContributions() is reliably closed, preventing resource leaks during SHA1 computation for uploads.

Changes:

• Wraps ContentResolver.openInputStream(...) in a Kotlin use {} block when computing the image SHA1.
• Adds a null-handling fallback when openInputStream(...) returns null.

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[github-actions]

✅ Generated APK variants!

• 🤖 Download prodDebugAPK
• 🤖 Download betaDebugAPK

[chrisdebian]

In the interest of being consistent with what we said on #6853: re-checked getSHA1() and it still closes the stream in its own finally block on every reachable path, so this isn't fixing an active leak. The one gap is if MessageDigest.getInstance("SHA1") throws NoSuchAlgorithmException, which returns before that finally runs — but SHA1 is a guaranteed algorithm on every JVM/Android implementation, so that's not reachable in practice either. The .use { } wrapper is harmless and does technically close the stream in that unreachable case too, so no objection to merging it, just flagging that it's a defensive addition rather than an actual leak fix.