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/tests/mysql/test_open.nim

@@ -0,0 +1,45 @@
+discard """
+  cmd: "nim c $file"
+"""
+
+# nim c -r tests/v2/mariadb/test_open.nim
+
+import std/unittest
+import ../../src/allographer/connection
+import ../../src/allographer/query_builder
+
+
+suite("MySQL connection"):
+  test("connection"):
+    let database = "database"
+    let user = "user"
+    let password = "pass"
+    let host = "mariadb"
+    let port = 3306
+    
+    let rdb = dbOpen(MySQL, database, user, password, host, port)
+    check(rdb.isConnected())
+
+
+  test("connection with URL"):
+    let url = "mysql://user:pass@mariadb:3306/database"
+    let rdb = dbOpen(MySQL, url)
+    check(rdb.isConnected())
+
+
+  test("connection with DatabaseUrl"):
+    let url = asDatabaseUrl("mysql://user:pass@mariadb:3306/database")
+    let rdb = dbOpen(MySQL, databaseUrl = url)
+    check(rdb.isConnected())
+
+
+  test("url is not start with mysql://"):
+    let url = "aaa://user:pass@mariadb:3306/database"
+    expect(ValueError):
+      discard dbOpen(MySQL, url)
+
+
+  test("cannot reach to database"):
+    let url = "mysql://john:password@host:0001/database"
+    expect(DbError):
+      discard dbOpen(MySQL, url)