chore(tests): update SPOT_1 slide, add SPOT_4, bump app versions to he-tme 1.2.0

- Replace SPOT_1 with breast cancer slide 1603ba4c (BREAST/BREAST_CANCER,
  6649×6578 at 0.25 MPP); preserve old 9375e3ed data as SPOT_4
- Add VIPS 10x resolution ambiguity note for SPOT_2, SPOT_3, SPOT_4
- Bump HETA_APPLICATION_VERSION to 1.2.0, TEST_APPLICATION_VERSION to 1.0.0
- Remove SPECIAL_APPLICATION concept; restore stress tests against test-app 1.0.0
- Unify payload builders via _build_wsi_input_item / _build_minimal_wsi_input_item
- Update SPOT_1_EXPECTED_RESULT_FILES sizes from staging run 43a3bcd2
- Reduce PIPELINE_NODE_ACQUISITION_TIMEOUT_MINUTES to 25

Author: ari-nz