Fix truncated content URI uploads

[zerox80]

Summary

Fixes #181 by preventing partially copied content:// upload cache files from being treated as valid upload sources.

Root cause

UploadFileFromContentUriWorker accepted any non-empty cache file. If the worker or process was interrupted while copying a large content:// file into local cache, a later retry could reuse that partial cache file, set the upload size from the truncated cache, and complete TUS successfully with the wrong bytes.

Changes

• Validate existing cached upload files against the original OCTransfer.fileSize before upload.
• Delete invalid cached files, clear stale TUS state, and recopy from the original content:// URI.
• Copy into a .part file first, validate the copied size, then rename into the final cache path only after validation succeeds.
• Add unit coverage for large exact sizes, partial non-zero cache files, larger-than-expected cache files, zero-byte cache files, and unknown expected sizes.

Validation

• git diff --cached --check passed before commit.
• ./gradlew.bat :opencloudApp:testOriginalDebugUnitTest could not run locally: JAVA_HOME is not set and no java executable is available in PATH.
• ./gradlew.bat :opencloudApp:compileOriginalDebugKotlin could not run locally for the same Java environment reason.