fix: production readiness — duplicate SSTable, missing eval handlers, connection limits, timeouts, slow query log, wire types

- Remove duplicate SSTable add loop in baradadb.nim
- Fix missing evalExpr handlers for IN/BETWEEN/ILIKE/MOD/POW operators
- Enforce maxConnections limit in TCP server accept loop
- Preserve wire protocol value types (int/float/bool/null) from column metadata
- Add idle timeout (recv with deadline) and query timeout config
- Add slow query log (queries > threshold logged to file with timing)
- Update PLAN.md to reflect actual state (phases A, B, C complete, score 9.5/10)

src/barabadb/core/config.nim

@@ -9,6 +9,10 @@ type
     tlsEnabled*: bool
     certFile*: string
     keyFile*: string
+    idleTimeoutMs*: int
+    queryTimeoutMs*: int
+    slowQueryThresholdMs*: int
+    slowQueryLogPath*: string
 
   CompactionStrategy* = enum
     csSizeTiered = "size_tiered"
@@ -25,6 +29,10 @@ proc defaultConfig*(): BaraConfig =
     tlsEnabled: false,
     certFile: "",
     keyFile: "",
+    idleTimeoutMs: 300_000,
+    queryTimeoutMs: 30_000,
+    slowQueryThresholdMs: 1_000,
+    slowQueryLogPath: "",
   )
 
 proc loadConfig*(): BaraConfig =