CR: Assigning/Unassigning an Examiner in a Registration needs popup when 2 examiners try to assign or unassign the same registration

**Description:
From Darius:**
The 'Unassign' button no longer triggers a confirmation pop-up. We need the pop-up back for when we unassign ourselves/other examiners from a file
Verified in new application pages and registration pages
**Additional note from Analyst:**
E.g., 2 examiners click into an unassigned Registration (renewal)
Examiner 1 assigns themselves to the Registration first
Examiner 2's Registration page has not updated with this information yet. Examiner 2 also assigns themselves to the Registration
Examiner 1 being assigned to the Registration is overwritten. Examiner 2 is now assigned to the Registration while Examiner 1 unknowingly continues to review the same Registration.

**What is the expected behaviour?:** 
If an examiner goes into a registration and clicks either 'Assign to Me' or 'Unassign';
If the assignee on that record is now different that what it was when they originally entered the page;
There is a pop-up notification that says 'The assignee on this record has changed. Refresh?' and when they select OK, the page refreshes and shows who is currently assigned to the record.

**Who is affected?:** 
Examiners

**How does the bug/issue affect your work as an
examiner?:**
Can cause overlap in work between Examiners

## Acceptance Criteria
> Generated by [Zenhub AI](https://www.zenhub.com/ai)

### Acceptance Criteria

**Scenario 2: Concurrency conflict when assigning a registration**
- **Given** Examiner A and Examiner B have both opened the same unassigned registration page
- **And** Examiner A clicks "Assign to Me" and successfully becomes the assignee
- **When** Examiner B clicks "Assign to Me" without having refreshed their page
- **Then** the system should detect that the assignee state has changed since the page was loaded
- **And** a pop-up notification must appear with the message: "The assignee on this record has changed. Refresh?"
- **And** no change to the database assignee should occur at this moment

**Scenario 3: Concurrency conflict when unassigning a registration**
- **Given** Examiner A and Examiner B have both opened the same registration page where Examiner A is currently assigned
- **And** Examiner B (or a system process) unassigns Examiner A or changes the assignee
- **When** Examiner A clicks "Unassign" on their stale page
- **Then** the system should detect that the assignee state has changed since the page was loaded
- **And** a pop-up notification must appear with the message: "The assignee on this record has changed. Refresh?"

**Scenario 4: Refreshing the page from the conflict popup**
- **Given** the conflict pop-up "The assignee on this record has changed. Refresh?" is currently displayed
- **When** the user selects "OK"
- **Then** the page should perform a full refresh
- **And** the registration page should now display the most current assignee information

**Scenario 5: Successful assignment when no conflict exists**
- **Given** I am an Examiner on a registration page
- **And** the assignee has not changed since I loaded the page
- **When** I click "Assign to Me"
- **Then** the registration should be successfully assigned to me without the conflict popup appearing