feat(registers): ST25DV RF_Ai_SS area-security register

Add St25dvRfAreaSS (Register) for the ST25DV per-area RF security
registers (RFA1SS..RFA4SS): pwd_ctrl (which RF password gates the area)
and rw_protection (read/write protection level). Bound via
tag.rf_area_ss(area) / tag.set_rf_area_ss(area, value). Modelled from
the model's own tested protection logic (single source of truth) and
cross-checked against _read_allowed / _write_allowed. 3 new tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_bitfield.py

@@ -11,6 +11,7 @@ from pm3py.sim import (
     Ntag5StatusReg, Ntag5ConfigReg, Ntag5LinkTag,
     NxpKeyPrivileges, IcodeDnaTag,
     IcodeFeatureFlags,
+    St25dvRfAreaSS, ST25DV04K,
 )
 
 
@@ -491,3 +492,30 @@ class TestIcodeFeatureFlags:
         text = repr(IcodeFeatureFlags(0x0001))
         assert "ICODE feature flags" in text
         assert "um_pp" in text
+
+
+class TestSt25dvRfAreaSS:
+    def test_fields(self):
+        r = St25dvRfAreaSS(0)
+        r.rw_protection = 2      # bits 3:2
+        r.pwd_ctrl = 1           # bits 1:0
+        assert int(r) == (2 << 2) | 1   # 0x09
+        assert r.rw_protection == "read+write need password"
+        assert r.pwd_ctrl == "RF_PWD_1"
+
+    def test_binding_matches_protection_logic(self):
+        tag = ST25DV04K()
+        r = St25dvRfAreaSS(0)
+        r.rw_protection = 3      # write locked
+        tag.set_rf_area_ss(1, r)
+        assert tag.rf_area_ss(1).rw_protection == "read needs password / write locked"
+        # the tag's existing protection logic must see the very same bits
+        assert tag._write_allowed(4) is False    # level 3 -> write forbidden
+        assert tag._read_allowed(4) is False     # level 3, no session -> read denied
+
+    def test_open_area(self):
+        tag = ST25DV04K()
+        tag.set_rf_area_ss(1, St25dvRfAreaSS(0))   # level 0 = fully open
+        assert tag.rf_area_ss(1).rw_protection == "open (read+write)"
+        assert tag._write_allowed(4) is True
+        assert tag._read_allowed(4) is True