fix: implement shadow copying for native binaries on Windows

[mynameistito]

Summary

This PR implements Shadow Copying for the bun-pty native binaries on Windows to resolve file-locking conflicts that cause the OpenCode Host to crash during multi-instance startup.

Changes

• Created src/plugin/pty/shadow.ts to handle copying the rust_pty.dll to a temporary directory and setting process.env.BUN_PTY_LIB.
• Refactored PTYManager in src/plugin/pty/manager.ts to lazy-load the bun-pty module only when needed, after ensuring the shadow copy is prepared.
• Updated ptySpawn tool in src/plugin/pty/tools/spawn.ts to support the now-async manager.spawn method.

Impact

• Fixes [Windows] Startup crash when opening multiple instances: EBUSY: failed copying files... package bun-pty #7: Prevents EBUSY errors when OpenCode attempts to verify plugins (especially those on @latest) while a PTY session is active.
• Improved Multi-instance Stability: Multiple instances of OpenCode can now start and verify their integrity without hitting locks on the PTY driver.

[mynameistito]

Please don't merge yet 😅

Edit: sweet it works as intended on Windows!

However maybe a little laggy if anyone else on Windows wants to check it out too that would be great :)