Fix TLS index and virtual reservation leaks on DLL unload

[jinpzhanAMD]

Summary
When mimalloc is statically linked into a DLL that is repeatedly loaded/unloaded, Application Verifier reports two resource leaks on DLL_PROCESS_DETACH. This PR fixes both.

Changes

1. Fix VERIFIER STOP 0x350 — TLS index not freed

mi_win_tls_slot_alloc() calls TlsAlloc() twice (for _mi_theap_default_slot and _mi_theap_cached_slot) but TlsFree() is never called on DLL unload.

Fix: Save the raw DWORD returned by TlsAlloc() into mi_tls_raw_default / mi_tls_raw_cached, and free them via mi_win_tls_slots_done() called from mi_process_done(). This avoids trying to reverse-engineer the original TLS index from mimalloc's internal slot representation, which is fragile and error-prone (e.g. expansion slots would compute wrong indices).

2. Fix VERIFIER STOP 0x903 — Virtual reservation leaked

mi_subproc_unsafe_destroy() only calls _mi_arenas_unsafe_destroy_all() for non-main subprocesses (guarded by if (subproc != &subproc_main)). When mi_subprocs_unsafe_destroy_all() destroys the main subproc, its arena virtual memory reservations (VirtualAlloc(MEM_RESERVE)) are never released via VirtualFree.

Fix: Add _mi_arenas_unsafe_destroy_all(&subproc_main) after mi_subproc_unsafe_destroy(&subproc_main) in mi_subprocs_unsafe_destroy_all().

3. Enable destroy_on_exit by default

Set mi_option_enable(mi_option_destroy_on_exit) in mi_process_init() so arena and page-map cleanup runs automatically on process/DLL shutdown, which is required for the DLL unload scenario.

Testing
Verified with Windows Application Verifier (leak checks enabled) on a DLL that statically links mimalloc. Both 0x350 and 0x903 verifier stops are resolved after these changes.

[daanx]

Thank you so much @jinpzhanAMD for the PR -- I added your suggestions in the latest dev3; hope this works now without leaks.