fix(database): hydrate deferred writes before staging values

[michalsn]

Description
This PR fixes deferred database writes so get() returns the pending value after set() or setMany() in the same request.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide