refactor(mobile): device asset entity to use modified time

[shenlong-tanwen]

Fixes #4939
Fixes #6439 (haven't tested the iOS part of the issue, the issue in Android does gets fixed)

Description

• The current hashing implementation of the app is follows:

  1. Get the list of assets from an album
  2. Get the existing hash of the asset from the platform specific entity - AndroidDeviceAssetSchema or IOSDeviceAssetSchema
  3. If the asset has an entry, re-use the hash and proceed to the next asset

  This approach has issues, especially when the asset is modified in-place outside immich after hashed by the app. When the asset is modified in-place and the platform does not make changes to the localID of the edited asset, our current approach proceeds to reuse the hash, even when the hash of the actual file is modified. The PR fixes this by also storing the asset's modifiedTime to the entity and compare it during lookup to reuse the hash.

• The existing approach also relied on updating object references inside collections to pass the updated hash back to the caller. This makes it hard to reason about the code. This has been refactored to make the logic simpler and understandable.

• Even when the localId from AssetEntity were Strings, we were using two different device asset schemas to store the hashes. One for android which converted the string IDs to int and the iOS that stored the string IDs directly. The PR refactors this to use a common entity named DeviceAssetEntitySchema. Migration handling is also added to move the hashes from the existing schemas to the new schemas.