rebuildIndex

        fn rebuildIndex(self: *Self, gpa: Allocator, ctx: Context) Oom!void {
            if (self.entries.capacity <= linear_scan_max) return;

            // We're going to rebuild the index header and replace the existing one (if any). The
            // indexes should sized such that they will be at most 60% full.
            const bit_index = try IndexHeader.findBitIndex(self.entries.capacity);
            const new_header = try IndexHeader.alloc(gpa, bit_index);
            if (self.index_header) |header| header.free(gpa);
            self.insertAllEntriesIntoNewHeader(if (store_hash) {} else ctx, new_header);
            self.index_header = new_header;
        }