Fix region tracker page leak and initial sizing

When allocating a new region tracker, we need to free the old one.
Also, when recreating the region tracker during repair, it has to be
large enough for the actual number of regions (which might be more
than INITIAL_REGIONS).

src/tree_store/page_store/page_manager.rs

@@ -1023,13 +1023,11 @@ impl Drop for TransactionalMemory {
         }
         let mut state = self.state.lock().unwrap();
         let tracker_len = state.allocators.region_tracker.to_vec().len();
-        let tracker_page_size = state
-            .header
-            .region_tracker()
-            .page_size_bytes(self.page_size);
-        if tracker_page_size < (tracker_len as u64) {
+        let tracker_page = state.header.region_tracker();
+        if tracker_page.page_size_bytes(self.page_size) < (tracker_len as u64) {
             drop(state);
             // Allocate a larger tracker page
+            self.free(tracker_page);
             if let Ok(tracker_page) = self.allocate(tracker_len) {
                 state = self.state.lock().unwrap();
                 state
@@ -1090,5 +1088,13 @@ mod test {
             }
         }
         txn.commit().unwrap();
+        drop(db);
+
+        let mut db = Database::builder()
+            .set_region_size((8 * page_size).try_into().unwrap())
+            .set_page_size(page_size)
+            .open(tmpfile.path())
+            .unwrap();
+        assert!(db.check_integrity().unwrap());
     }
 }

src/tree_store/page_store/region.rs

@@ -7,7 +7,7 @@ use crate::tree_store::page_store::page_manager::{INITIAL_REGIONS, MAX_MAX_PAGE_
 use crate::tree_store::page_store::xxh3_checksum;
 use crate::tree_store::PageNumber;
 use crate::Result;
-use std::cmp;
+use std::cmp::{self, max};
 use std::mem::size_of;
 
 const REGION_FORMAT_VERSION: u8 = 1;
@@ -133,7 +133,8 @@ pub(super) struct Allocators {
 impl Allocators {
     pub(super) fn new(layout: DatabaseLayout) -> Self {
         let mut region_allocators = vec![];
-        let mut region_tracker = RegionTracker::new(INITIAL_REGIONS, MAX_MAX_PAGE_ORDER + 1);
+        let initial_regions = max(INITIAL_REGIONS, layout.num_regions());
+        let mut region_tracker = RegionTracker::new(initial_regions, MAX_MAX_PAGE_ORDER + 1);
         for i in 0..layout.num_regions() {
             let region_layout = layout.region_layout(i);
             let allocator = BuddyAllocator::new(