Summary

This PR updates Immich asset uploads to use streamed multipart encoding to prevent high memory usage (and potential OOM) during uploads.

Closes #1033

Problem

Uploads to Immich were sent via requests.post(..., files=...) in ClassImmichPhotos.push_asset(...).
With large files and/or concurrent uploads, multipart payload handling could cause excessive RAM usage.

Changes

• Switched Immich upload implementation in push_asset to streamed multipart using MultipartEncoder
• Kept existing upload metadata fields and duplicate handling behavior unchanged
• Preserved optional sidecar upload support
• Ensured file handles are safely managed during upload (ExitStack)

Scope / Impact

This affects all upload flows that call ClassImmichPhotos.push_asset(...), including:

• automatic migration uploads to Immich
• album uploads
• no-album uploads

Tests

• Added focused regression tests:
  • tests/test_immich_upload_streaming.py
  • verifies multipart streaming is used
  • verifies no files= argument is used
  • verifies sidecar inclusion still works
• Ran:
  • uv run python -m unittest tests.test_immich_upload_streaming ✅
  • uv run python -m unittest (contains existing unrelated baseline failures)