fix(ventus): add missing reinit function to ensure proper device cleanup

[menxb]

Problem

Currently, the Ventus device in POCL has ops->reinit set to NULL, which causes pocl_uninit_devices() to skip the cleanup process for Ventus devices. This results in a resource leak where vt_dev_close() is never called, preventing proper device cleanup.

Solution

This PR adds the missing pocl_ventus_reinit() function to ensure proper device lifecycle management:

• Add pocl_ventus_reinit function to fix uninit not being called issue
• Implement proper device re-initialization with hardware connectivity reset
• Reset command queue state and device connection
• Ensure ventus device follows pocl device management lifecycle
• Fix resource leak where vt_dev_close was not called due to missing reinit

Key Changes

• Added pocl_ventus_reinit() function in pocl_ventus.cc
• Added function declaration in pocl_ventus.h
• Set ops->reinit = pocl_ventus_reinit instead of NULL

Technical Details

The reinit function:

1. Safely closes existing device connection (vt_dev_close)
2. Re-opens the device connection (vt_dev_open)
3. Resets command queue state (ready_list, command_list, current_kernel)
4. Handles proper error checking and logging

Testing

• Verified that device cleanup now works properly
• Confirmed vt_dev_close() is called during uninit process

Fixes issue where pocl_uninit_devices skips ventus device cleanup because ops->reinit was NULL, preventing proper resource cleanup.