feat(Pausable)!: make `pa_[un]pause` return `bool`

[mooori]

Makes pa_pause and pa_unpause return a bool that indicates whether the feature is newly (un)paused. This corresponds to the return values of std::collections::HashSet methods insert and remove.

Closes this external issue.

Other changes: events

This PR also changes event emitting behavior. Sneaking it into this PR since it only reorders code in the two functions that are modified here.

Previously events Pause and Unpause were emitted even if:

• State was not modified since the feature was alreay (un)paused.
• The function panicked because state could not be serialized.

To avoid this, code that emits events has been moved past actions that may fail.

Breaking changes

• pa_pause and pa_unpause return bool (previously no return value).
• Pause and Unpause events are only emitted when state is successfully modified.