Fix: Additional unicode characters getting added to pinned items

[batsdk]

Fix unicode/garbled text on paste from browsers and Notes

Two fixes:

1. Clipboard.swift — strips metadata-only pasteboard types (Chrome's customWebKitPasteboardData, chromiumSourceToken, Notes' notesRichText, etc.) before storing. These tags travel alongside the real content but
   confuse paste targets, producing garbled or extra characters.
2. History.swift — deep-copies HistoryItemContent objects when merging a duplicate item, instead of sharing the reference. The old item is deleted from Core Data immediately after, which was silently invalidating the
   shared content objects and leaving the new item with blank/corrupted data.

[weisJ]

Can you elaborate on what issue this is solving?

[weisJ]

Maccy deliberatly doesn't strip these types unless pasting without formatting is enabled. Some of those are needed for specific features for the relevant applications to function properly.