gh-112532: Tag mimalloc heaps and pages (#113742)

* gh-112532: Tag mimalloc heaps and pages

Mimalloc pages are data structures that contain contiguous allocations
of the same block size. Note that they are distinct from operating
system pages. Mimalloc pages are contained in segments.

When a thread exits, it abandons any segments and contained pages that
have live allocations. These segments and pages may be later reclaimed
by another thread. To support GC and certain thread-safety guarantees in
free-threaded builds, we want pages to only be reclaimed by the
corresponding heap in the claimant thread. For example, we want pages
containing GC objects to only be claimed by GC heaps.

This allows heaps and pages to be tagged with an integer tag that is
used to ensure that abandoned pages are only claimed by heaps with the
same tag. Heaps can be initialized with a tag (0-15); any page allocated
by that heap copies the corresponding tag.

* Fix conversion warning

Include/internal/mimalloc/mimalloc/internal.h

@@ -155,7 +155,7 @@ size_t     _mi_bin_size(uint8_t bin);           // for stats
 uint8_t    _mi_bin(size_t size);                // for stats
 
 // "heap.c"
-void       _mi_heap_init_ex(mi_heap_t* heap, mi_tld_t* tld, mi_arena_id_t arena_id);
+void       _mi_heap_init_ex(mi_heap_t* heap, mi_tld_t* tld, mi_arena_id_t arena_id, bool no_reclaim, uint8_t tag);
 void       _mi_heap_destroy_pages(mi_heap_t* heap);
 void       _mi_heap_collect_abandon(mi_heap_t* heap);
 void       _mi_heap_set_default_direct(mi_heap_t* heap);

Include/internal/mimalloc/mimalloc/types.h

@@ -311,6 +311,7 @@ typedef struct mi_page_s {
   uint32_t              slice_offset;      // distance from the actual page data slice (0 if a page)
   uint8_t               is_committed : 1;  // `true` if the page virtual memory is committed
   uint8_t               is_zero_init : 1;  // `true` if the page was initially zero initialized
+  uint8_t               tag : 4;           // tag from the owning heap
 
   // layout like this to optimize access in `mi_malloc` and `mi_free`
   uint16_t              capacity;          // number of blocks committed, must be the first field, see `segment.c:page_clear`
@@ -551,6 +552,7 @@ struct mi_heap_s {
   size_t                page_retired_max;                    // largest retired index into the `pages` array.
   mi_heap_t*            next;                                // list of heaps per thread
   bool                  no_reclaim;                          // `true` if this heap should not reclaim abandoned pages
+  uint8_t               tag;                                 // custom identifier for this heap
 };