fix(android): use app cache dir for saveToTempFile

[msluszniak]

Description

std::filesystem::temp_directory_path() resolves $TMPDIR to /data/local/tmp on Android <13. App processes can't write there, so every saveToTempFile call path (style transfer, text-to-image) fails with code: 103, "Failed to save the image: /data/local/tmp/rn_executorch_*.png".

This PR pipes the platform-provided app cache directory (reactApplicationContext.cacheDir on Android, NSTemporaryDirectory() on iOS) through injectJSIBindings and uses it in saveToTempFile instead of std::filesystem::temp_directory_path().

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 the computer-vision example app on an Android 12 device (or earlier). If you don't have any, please contact me.
2. Open the Style Transfer demo, pick an image, run the model.
3. Verify the styled image is saved and displayed without the code: 103 error.
4. Sanity-check on iOS and a newer Android (13+) to confirm no regression.

Related issues

Fixes #962