feat: clean build + crossmodal.tla + TLA+ symmetry (v1.0.0-prep)

Build warnings cleanup (0 warnings):
- Suppress threadpool deprecation warning (baradadb.nim)
- Remove unused 'os' import (logging.nim)
- Fix ImplicitDefaultValue for newNode params (ast.nim)
- Add explicit cstring cast for posix.open (wal.nim)
- Fix HoleEnumConv for MsgKind parsing (server.nim)

TLA+ Formal Verification:
- Add symmetry reduction (Permutations) to all 9 existing specs
- Add SYMMETRY directive to all .cfg files
- New crossmodal.tla: cross-modal consistency spec
  * MetadataVectorConsistency, HybridResultValid
  * CommittedAtomicity, AbortedAtomicity, TxnStateValid
- New models/crossmodal.cfg

Tests:
- Add Cross-Modal TLA+ Faithfulness tests (4 tests)

Docs:
- Update PLAN.md and BUG_AUDIT.md with completed tasks

formal-verification/models/backup.cfg

@@ -18,3 +18,4 @@ INVARIANTS
   RetentionInvariant
   HistoryConsistency
   BackupIdValid
+SYMMETRY Symmetry

formal-verification/models/crossmodal.cfg

@@ -0,0 +1,23 @@
+CONSTANTS
+  Entities = {e1, e2}
+  Participants = {p1, p2}
+  Doc = Doc
+  Vec = Vec
+  Graph = Graph
+  Fts = Fts
+  MaxSteps = 6
+  Nil = Nil
+
+SPECIFICATION Spec
+
+CHECK_DEADLOCK FALSE
+
+INVARIANTS
+  TypeOk
+  MetadataVectorConsistency
+  HybridResultValid
+  CommittedAtomicity
+  AbortedAtomicity
+  TxnStateValid
+
+SYMMETRY Symmetry

formal-verification/models/deadlock.cfg

@@ -12,3 +12,4 @@ INVARIANTS
   TypeOk
   GraphIntegrity
   NoSelfLoops
+SYMMETRY Symmetry

formal-verification/models/gossip.cfg

@@ -13,3 +13,4 @@ INVARIANTS
   IncarnationMonotonic
   DeadConsistency
 
+SYMMETRY Symmetry

formal-verification/models/mvcc.cfg

@@ -19,3 +19,4 @@ INVARIANTS
 
 PROPERTIES
   CommitProgress
+SYMMETRY Symmetry

formal-verification/models/raft.cfg

@@ -17,3 +17,4 @@ INVARIANTS
   LogMatching
   LeaderHasSelfHeartbeat
 
+SYMMETRY Symmetry

formal-verification/models/recovery.cfg

@@ -16,3 +16,4 @@ INVARIANTS
   RedoCommitted
   RecoveryCompleteness
   WalIntegrity
+SYMMETRY Symmetry

formal-verification/models/replication.cfg

@@ -16,3 +16,4 @@ INVARIANTS
 
 PROPERTIES
   MonotonicLsn
+SYMMETRY Symmetry

formal-verification/models/sharding.cfg

@@ -15,3 +15,4 @@ INVARIANTS
   VirtualNodeMapping
   NodeAssignmentConsistency
   VnodeOrdering
+SYMMETRY Symmetry

formal-verification/models/twopc.cfg

@@ -16,3 +16,4 @@ INVARIANTS
   ParticipantStateValid
   RecoveryConsistency
 
+SYMMETRY Symmetry