Refactor shift constraints in tests to use new constraint classes

- Updated test cases in `test_workers.py` to replace dictionary-based constraints with instances of `PreShiftConstraint`, `PostShiftConstraint`, and `MaxShiftsPerWeekConstraint`.
- Added a new test `test_worker_assign_as_block_preference2` to verify worker preferences for block assignments.
- Marked tests as slow where appropriate to improve test suite performance.

gen_cons.py

@@ -3,7 +3,7 @@ import datetime
 import os
 import sys
 import time
-from rota.shifts import NoWorkers, RotaBuilder, SingleShift, WorkerRequirement, days
+from rota.shifts import NoWorkers, PostShiftConstraint, PreShiftConstraint, RotaBuilder, SingleShift, WorkerRequirement, days
 import typer
 import subprocess
 import pandas as pd
@@ -335,7 +335,7 @@ def main(
             days=days,
             balance_offset=2,
             assign_as_block=False,
-            constraint=[
+            constraints=[
                 #{
                 #    "name": "max_shifts_per_week",
                 #    "options": 3,
@@ -349,9 +349,11 @@ def main(
             length=12.5,
             days=days[5:],
             balance_offset=1,
-            constraint=[
+            constraints=[
                 #{"name": "pre", "options": 2},
-                {"name": "post", "options": 1},
+                
+                #{"name": "post", "options": 1},
+                PostShiftConstraint(days=1, start_date="2025-11-24"),
             ],
             display_char="a",
             #force_assign_with=["oncall"]
@@ -380,7 +382,7 @@ def main(
             length=12.5,
             days=days[:5],
             balance_offset=1,
-            constraint=[
+            constraints=[
                 #{"name": "pre", "options": 1},
                 #{"name": "post", "options": 1},
             ],