Move NewTestCoseSigner to cose package

[eccles]

Test Results

robot:smoke: RESULTS: Tests 96 , Errors 0 , Failures 0 , Time 47.064
robot:core: RESULTS: Tests 533 , Errors 0 , Failures 0 , Time 187.060
robot:tenancies: RESULTS: Tests 38 , Errors 0 , Failures 0 , Time 81.975
robot:invites: RESULTS: Tests 23 , Errors 0 , Failures 0 , Time 6.353
robot:scitt: RESULTS: Tests 8 , Errors 0 , Failures 0 , Time 173.628
robot:abac: RESULTS: Tests 196 , Errors 0 , Failures 0 , Time 164.494
robot:obac: RESULTS: Tests 117 , Errors 0 , Failures 0 , Time 253.801
robot:slow-cd: RESULTS: Tests 4 , Errors 0 , Failures 0 , Time 23.492
robot:flaky: RESULTS: Tests 4 , Errors 0 , Failures 1 , Time 10.738
RESULTS: Tests 8 , Errors 0 , Failures 0 , Time 0.999

playright:api:smoke:   34 passed (47.4s)
playright:api:core:   41 passed (41.8s)
playright:api:app-registrations:   44 passed (39.8s)
playright:api:membership:   69 passed (54.8s)
playright:api:tenancies:   61 passed (27.6s)
playright:ui:authentication:   6 passed (55.7s)
playright:ui:management:   3 passed (20.0s)

AB#10597