Users needs functions to count the number of free and used entries.
1. `nvs_get_stats()` This function return structure of statistic about the uspace NVS.
(Struct: used_entries, free_entries, total_entries and namespace_count)
2. `nvs_get_used_entry_count()` The second function return amount of entries in the namespace (by handler)
3. Added unit tests.
Closes TW<12282>
When read caching was added, Page::findItem started modifying itemIndex reference argument even if item wasn't found.
Incidentally, Storage::findItem reused itemIndex when starting search at next page.
So,
- if the first page had a cached index (findItem was called for that page), and it pointed to a non-zero index,
- first page has a few empty items at the end (but is marked full),
- next search looked up the item on the second page,
- index of the item on the second page was less than the cached index on the first page,
then the search would fail because cached starting index was reused.
This change fixes both sides of the problem:
- Page::findItem shouldn't modify itemIndex argument if item is not found
- Storage::findItem should not reuse itemIndex between pages
Two tests have been added.
Introduces new internal function, Page::alterEntryRangeState, which gathers changes to multiple elements of entry state table into a single write, provided that these changes fall into a single word. This allows changing state of up to 16 entries in a single write.
Also adds new function, writeEntryData, which writes the whole payload of SZ and BLOB type entries in one go, instead of splitting it into multiple 32-byte writes.
This reduces number of writes required for SZ and BLOB entries.
