feat: migrate refimpls from draft-00 to draft-01 claim names

- Rename `par` to `pred` (predecessor) in types, serialization, tests
- Remove `pol`, `pol_decision` from core payload; move to `ect_ext`
- Remove `sub` from payload (not part of ECT spec)
- Update `typ` from `wimse-exec+jwt` to `exec+jwt` (accept both)
- Rename MaxParLength to MaxPredLength everywhere
- Update testdata, demos, READMEs with migration table
- All Go tests pass, all 56 Python tests pass (90% coverage)

refimpl/python/tests/test_ledger_extra.py

@@ -4,12 +4,12 @@ import time
 
 import pytest
 
-from ect import Payload, MemoryLedger, ErrTaskIDExists, POL_DECISION_APPROVED
+from ect import Payload, MemoryLedger, ErrTaskIDExists
 
 
 def test_ledger_append_and_get():
     m = MemoryLedger()
-    p = Payload(iss="i", aud=["a"], iat=1, exp=2, jti="j1", exec_act="act", par=[])
+    p = Payload(iss="i", aud=["a"], iat=1, exp=2, jti="j1", exec_act="act", pred=[])
     seq = m.append("jws1", p)
     assert seq == 1
     assert m.get_by_tid("j1").jti == "j1"
@@ -17,7 +17,7 @@ def test_ledger_append_and_get():
 
 def test_ledger_err_task_id_exists():
     m = MemoryLedger()
-    p = Payload(iss="i", aud=["a"], iat=1, exp=2, jti="j-dup", exec_act="e", par=[])
+    p = Payload(iss="i", aud=["a"], iat=1, exp=2, jti="j-dup", exec_act="e", pred=[])
     m.append("jws1", p)
     with pytest.raises(ErrTaskIDExists):
         m.append("jws2", p)
@@ -25,7 +25,7 @@ def test_ledger_err_task_id_exists():
 
 def test_ledger_contains_wid():
     m = MemoryLedger()
-    p = Payload(iss="i", aud=["a"], iat=1, exp=2, jti="j1", exec_act="e", par=[], wid="wf1")
+    p = Payload(iss="i", aud=["a"], iat=1, exp=2, jti="j1", exec_act="e", pred=[], wid="wf1")
     m.append("jws", p)
     assert m.contains("j1", "") is True
     assert m.contains("j1", "wf1") is True