Feature: Add "Update" mode to Steam Importer

[Laudenlaruto]

This PR introduces a new "Update" mode for the Steam importer, allowing users to sync progress (playtime) and status for existing games without overwriting custom metadata or resetting completed games.

Following up on PR #711

Key Changes:

• Backend (steam.py):

  • Implemented _update_existing_game to handle syncing progress and status.
  • Updated _process_game to support the new update mode.
  • Refined new mode to strictly skip existing items (previously it might have processed them depending on flow).
  • Added logic to protect "Completed" or "Dropped" statuses from being overwritten by the importer, while still updating playtime.

• Frontend (import_data.html):

  • Added "Sync New Items and Update Existing" (value="update") option to the import settings dropdown.

• Testing (test_steam_update.py):

  • Added comprehensive tests covering:
    • Updating progress and status for "Planning" or "In Progress" games.
    • Ensuring "Completed" games update playtime but retain their status.
    • Verifying that "New" mode ignores existing games entirely.

How to Test:

• Navigate to the Import page
• Select "Sync New Items and Update Existing" from the Import Mode dropdown.
• Run a Steam import.
• Verify that:
  • New games are added.
  • Existing games have their playtime updated.
  • Existing

Games marked as "Completed" do not revert to "In Progress" even if playtime increased.

My concern:

• Introducing the "update" mode will possibly mislead or even break import from other provider (Trakt, AniList, MAL, IMDB, etc.) There are a couple of ways to tackle this :
  • Either update the should_process_media to default back to new with a warning for source that don't support this method
  • Implement "Update" logic for all other importers (Trakt, AniList, etc.) to handle the new mode.

WDYT ?