Address space from ring buffer memory mapped into user space should be cleaned up

### Describe the bug

Currently the memory mapping for ring buffers is never cleaned up (until the process exits). This is only a leak of address space in the user process, not memory, but we should return a handle the user-space process can use to release the mapping.

### OS information

_No response_

### Steps taken to reproduce bug

1. Repeatedly open and close a ring buffer

### Expected behavior

After closing the ring buffer, the address space in the user process should be released.

### Actual outcome

The address space stays reserved until the process exits.

### Additional details

_No response_