(a) Who May Testify.
Any person may be a witness in any action or proceeding under these rules except as hereinafter provided or as provided in the Rules of Evidence.
(b) When Excused.
A witness subpoenaed to attend in a criminal case is dismissed and excused from further attendance as soon as he or she has given his or her testimony in chief and has been cross-examined thereon, unless either party makes request in open court that the witness remain in attendance; and witness fees will not be allowed any witness after the day on which his or her testimony is given, except when the witness has in open court been required to remain in further attendance.
(c) Persons Incompetent To Testify.
The following persons are incompetent to testify: (1) those who are of unsound mind, or intoxicated at the time of their production for examination; and (2) those who do not have the capacity of receiving just impressions of the facts about which they are examined or who do not have the capacity of relating them truly. This shall not affect any recognized privileges.
(d) Not Excluded on Grounds of Interest.
No person offered as a witness shall be excluded from giving evidence by reason of his or her interest in the result of the action, as a party thereto or otherwise, but such interest may be shown to affect his or her credibility.