feat(z3): zero-error SMT-LIB2 output + BMC verify blocks for KRaft

- Declare speckl_len_Int helper for list/sequence lengths
- Fix infix = inside => bodies (final pass regex)
- Handle prime notation: currentTerm' → currentTerm_post
- Handle length() calls: length(log) → (speckl_len_Int log)
- Handle min(): (ite (<= a b) a b) instead of unsupported 'min'
- Handle subtraction: i-1 → (- i 1)
- Declare _post state vars when invariants compare pre/post
- Added 3 BMC verify blocks to KRaft spec (TermMonotonicity, CommitSafety, LeaderCompleteness)
- Z3 returns clean sat with zero errors for all specs
- All 37 tests pass

compiler/test-output/RetryHandler.specbom.cdx.json

@@ -38,7 +38,7 @@
         "name": "Scott Scoble",
         "email": "scott@scoble.me"
       },
-      "timestamp": "2026-05-10T05:38:34.907Z"
+      "timestamp": "2026-05-10T06:07:50.700Z"
     },
     {
       "subject": "speck:RetryHandler",
@@ -53,7 +53,7 @@
         "name": "Speckl Compiler",
         "email": "compiler@speckl.scoble.me"
       },
-      "timestamp": "2026-05-10T05:38:34.907Z"
+      "timestamp": "2026-05-10T06:07:50.700Z"
     },
     {
       "subject": "speck:RetryHandler",
@@ -68,7 +68,7 @@
         "name": "Speckl Compiler",
         "email": "compiler@speckl.scoble.me"
       },
-      "timestamp": "2026-05-10T05:38:34.907Z"
+      "timestamp": "2026-05-10T06:07:50.700Z"
     }
   ]
 }