feat(clients): add nim-allographer client with BaraDB driver support

- Pure Nim wire protocol client (async + sync, no C FFI)
- Query Builder: fluent API, SQL generator, execution, transactions
- Schema Builder: create/alter/drop tables, column operations
- Connection pool with aging and timeout handling
- ORM integration via compile-time DB_BARADB switch
- Tests: test_open, test_query
- Documentation: README.md, PLAN_BARADB.md

clients/nim-allographer/example/database/migrations/migrate.nim

@@ -0,0 +1,12 @@
+import std/asyncdispatch
+import ../../../src/allographer/schema_builder
+import ../connection
+import ./init_databaase
+import ./create_all_type_table
+
+proc migrate*() =
+  initDatabaase()
+  createAllTypeTable()
+
+migrate()
+createSchema(rdb).waitFor()