State tax filing

Here are the requirements to claim Washington Residency:

Persons are considered residents of this state for sales and use tax purposes if they take actions which indicate that they intend to live in this state on more than a temporary or transient basis. A person may be considered a resident of this state even though the person is a resident of another state.

The Department of Revenue presumes that a person is a resident of this state if he or she does any of the following:

• Maintains a residence in Washington for personal use;
• Lives in a motor home or vessel which is not permanently attached to any property if the person previously lived in this state and does not have a permanent residence in any other state;
• Is registered to vote in this state;
• Receives benefits under one of Washington's public assistance programs;
• Has a state professional or business license in this state;
• Is attending school in this state and paying tuition as a Washington resident or is a custodial parent with a child attending a public school in this state;
• Uses a Washington address for federal or state taxes;
• Has a Washington State driver's license; or
• Claims Washington as a residence for obtaining a hunting or fishing license, eligibility to hold public office or for judicial actions.

You could probably take the earlier date of April 3, 2023 as the date of beginning WA residency, as you suggested.  Here's some info to help you file a Part-Year Resident Return for Arizona.