Issue #1872 fix - FUSE-T usb stick unmounting

[askaine]

Fix macOS FUSE-T process leak preventing volume unmount and USB ejection

Summary

When dismounting a VeraCrypt volume on macOS using a FUSE-T build, the background user-space NFS daemon (go-nfsv4) often fails to exit its event loop (fuse_main()). As a result, active file descriptors remain open on the underlying block device, causing hdiutil detach and subsequent disk ejection (diskutil eject) to fail with "resource busy" or unmount dissent errors.

Error Log / Reproduction

Attempting to eject the underlying drive in the terminal after unmounting via the VeraCrypt GUI results in:

Unmount of disk4 failed: at least one volume could not be unmounted
Unmount was dissented by PID 9572 (/Library/Application Support/fuse-t/bin/go-nfsv4-1.2.7)
Dissenter parent PPID 1 (/sbin/launchd)

Proposed Changes

PID Tracking (src/Core/Unix/FuseService.cpp): Write the FUSE service process ID to /tmp/veracrypt_fuset_slot_.pid immediately before entering fuse_main().

Forced Teardown

(src/Core/Unix/CoreMacOs.cpp): In CoreMacOSX::DismountVolume, check for the saved PID file and terminate the lingering go-nfsv4 / FUSE-T daemon before issuing hdiutil detach. This guarantees file handles are released prior to device detachment.

Testing & Verification Request

Note: These changes were authored and cross-referenced from a Windows environment. Opening as a Draft PR to request code review and runtime testing from maintainers or macOS users with FUSE-T setups.