* Break backwards compatibility
* Allow to deserialize only base-data of packages and build
actions to potentially speed up showing tables
* Speed up package search in many cases by only deserializing
base-data (unless details are actually wanted)
* Avoid creation of map with all archive contents; instead parse packages
while walking though the archive
* Avoid instantiation of std::string in come cases (using std::string_view)
* Reuse libarchive's archive entry when walking though archive
* Use visitor-based database parser in all places to avoid intermediate big
array with all package objects
Especially when enabling files DBs it is quite problematic to store all
package objects of a database within one big array. This change avoids the
array and instead adds the packages directly. The disadvantage is that
clearing the database isn't as simple anymore.
* Avoid keeping list of all packages in memory by pushing each package
directly to the JSON array
* Avoid check for database before pushing each package; do it only before
reaching the next database
* Remove no longer required functions
* Only lock the config for writing the reloading the config file
* Make sure all write operations to the database acquire an "update mutex"
to ensure only one write operation happens at a time
* Do *not* acquire any additional locks when reading from a database as it
should be safe to do so even when a write operation happens because
* LMDB read and write transactions can happen at the same time
* The package cache has its own mutex anyways
* Write ops to the package cache try to lock the "update mutex" to
prevent writing "old" data to the cache during updates
* Make "lastUpdate" atomic to avoid locking the config when accessing it
It is about
```
return result_type{ storageEntry.id, storageEntry.ref.relatedStorage };
```
but it isn't clear why the compiler thinks there's a problem.
* Treat an empty archive buffer/file as error as this should never happen
and it is better to fail early than replacing existing data with nothing
* Query error message also when opening archive from file
Martchus