PSS: Change from `Commit`-on-`Close` convention to explicit calls and make `Close` errors non-critical

[iamandrii]

The Enhancement

At first, it was thought that Commit-on-Close convention would be more preferable, than others, but after some time, it is clear that this introduces more problems than convenience, for example, it is hard to make a normal error catching + defer for Close, because the Commit is made during Close.

The Proposal

Split logic into two methods -- Commit and Close, make Close do not return any errors (but still return nil to conform to default APIs)