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

src/barabadb/query/ast.nim

@@ -459,7 +459,7 @@ type
     of nkStatementList:
       stmts*: seq[Node]
 
-proc newNode*(kind: NodeKind, line, col: int = 0): Node =
+proc newNode*(kind: NodeKind, line: int = 0, col: int = 0): Node =
   result = Node(kind: kind, line: line, col: col)
   case kind
   of nkSelect: result.selResult = @[]