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/transaction.nim

@@ -0,0 +1,56 @@
+import json, asyncdispatch, strformat
+import ../src/allographer/schema_builder
+import ../src/allographer/query_builder
+import ./connections
+import ./setup
+
+
+proc main(){.async.} =
+  rdb.create(
+    table("auth",[
+      Column.increments("id"),
+      Column.string("auth")
+    ]),
+    table("users",[
+      Column.increments("id"),
+      Column.string("name").nullable(),
+      Column.string("email").nullable(),
+      Column.string("address").nullable(),
+      Column.foreign("auth_id").reference("id").onTable("auth").onDelete(SET_NULL)
+    ])
+  )
+
+  # seeder
+  seeder(rdb, "auth"):
+    rdb.table("auth").insert(@[
+      %*{"auth": "admin"},
+      %*{"auth": "user"}
+    ]).waitFor
+
+  seeder(rdb, "users"):
+    var users: seq[JsonNode]
+    for i in 1..10:
+      let authId = if i mod 2 == 0: 2 else: 1
+      users.add(
+        %*{
+          "name": &"user{i}",
+          "email": &"user{i}@gmail.com",
+          "auth_id": authId
+        }
+      )
+    rdb.table("users").insert(users).waitFor
+
+  echo "====="
+  transaction(rdb):
+    assert rdb.isInTransaction == true
+    echo rdb.select("name", "email").table("users").where("id", "=", 2).get().await
+
+  echo "====="
+  transaction(rdb):
+    assert rdb.isInTransaction == true
+    rdb.table("table").insert(%*{"aaa": "bbb"}).await
+    echo rdb.table("aaa").get().await
+
+  assert rdb.isInTransaction == false
+
+main().waitFor