fix: reduce ram usage

[sesky4]

Summary

Hi, I found Maccy uses ~2.4 GB of memory at startup on my machine with a large clipboard history (hundreds of items with images/RTF blobs). Others have reported the same issue (#1240 #1294 #1129 #1088). This PR reduces startup memory.

Issues

1. Unbounded fetch — History.load() uses a FetchDescriptor<HistoryItem>() with no fetchLimit, eagerly loading every row and all contents relationships into memory.
2. Inline blob storage — HistoryItemContent.value stores image/RTF blobs inline in SQLite, so every fetch hydrates all of them into __DataStorage._bytes.
3. Full-table fetch on every copy — findSimilarItem() does another unbounded FetchDescriptor<HistoryItem>() per clipboard change for dedup.
4. Eager thumbnail generation — ensureThumbnailImage() decodes full-resolution NSImage for every row during view construction, even when the popup isn't visible.

Changes

• HistoryItemContent.value: add @Attribute(.externalStorage) so blobs are stored out-of-line and loaded lazily.
• History.load(): separate pinned (unlimited) and unpinned (fetchLimit = min(size, 50)) fetches, each sorted by the user's sort order.
• findSimilarItem(): search the in-memory all array instead of doing a full-table fetch.
• HistoryItemView: gate ensureThumbnailImage() on scenePhase == .active.

Testing

macOS 26.5.1, 1,140 items in DB (SQLite file ~2.8 GB).

Metric	Before	After
Physical footprint	2.4 GB	59 MB
RSS	~2.4 GB	116 MB

Filling 999 slots with fresh text copies kept memory stable at ~59 MB. Pins, search, delete, paste stack all work.

Backward compatibility

@Attribute(.externalStorage) triggers a transparent Core Data migration on first launch. Existing data is preserved — no data loss.

[weisJ]

1. Unbounded fetch — History.load() uses a FetchDescriptor<HistoryItem>() with no fetchLimit, eagerly loading every row and all contents relationships into memory

Your fix just effectively sets the history limit to 50. How are you handling if someone wants to search for content older than the last 50 entries?

2. Inline blob storage — HistoryItemContent.value stores image/RTF blobs inline in SQLite, so every fetch hydrates all of them into __DataStorage._bytes.

Do you have data that Attribute(.externalStorage) on its own reduces the memory footprint? Where do you have the information from that it will not load the data into memory?

3. Full-table fetch on every copy — findSimilarItem() does another unbounded FetchDescriptor<HistoryItem>() per clipboard change for dedup.

Already handled in #1441. Note that while this improves performance when copying I found to real effect of it on memory usage.

4. Eager thumbnail generation — ensureThumbnailImage() decodes full-resolution NSImage for every row during view construction, even when the popup isn't visible.

Thumbnails are generated as soon as an item is displayed. Not on view creation.