feat(nvs): Allow read-only NVS partitions smaller than 0x3000

E.g. for factory settings data

Closes https://github.com/espressif/esp-idf/issues/15317

components/nvs_flash/host_test/nvs_page_test/main/test_fixtures.hpp

@@ -110,7 +110,7 @@ public:
         size_t columns = size / column_size;
         size_t column;
 
-        for(column = 0; column < columns; column = column + 1)
+        for(column = 0; column < columns; ++column)
         {
             // read column
             if((err = esp_partition_read_raw(&esp_partition, dst_offset + (column * column_size), buff, column_size)) != ESP_OK) return err;

components/nvs_flash/src/nvs_pagemanager.cpp

@@ -124,8 +124,8 @@ esp_err_t PageManager::load(Partition *partition, uint32_t baseSector, uint32_t
         }
     }
 
-    // partition should have at least one free page
-    if (mFreePageList.empty()) {
+    // partition should have at least one free page if it is not read-only
+    if (!partition->get_readonly() && mFreePageList.empty()) {
         return ESP_ERR_NVS_NO_FREE_PAGES;
     }