Please squash merge this PR

Description

The repro is the same: Bug Repro Instructions

Open bed nights page in two windows for the same project
In one window, click remove on an existing assigned client
In the other window, click remove on the same client
- Previously result: unexplained error
- New result: appears successful and refreshes

This also adds tests for BulkRemoveService, and updates the BulkAssignService tests to ensure permissions are checked against the project entity.

[x] I have performed a self-review of my code
[x] I have run the code that is being changed under ideal conditions, and it doesn't fail
[x] My code includes comments and/or descriptive variable names to help other engineers understand the intent (or not applicable)
[x] My code follows the style guidelines of this project (rubocop)
[x] I have updated the documentation (or not applicable)
[x] If it's not obvious how to test this change, I have provided testing instructions in this PR or the related issue