PHPDoc: Replace non-existing type pair with array
Summary:
`pair` is not a valid type. See https://docs.phpdoc.org/guide/references/phpdoc/types.html.
Phorge counterpart to D26069.
Test Plan: Read docs; run static code analysis; get 35 errors less.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26084