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/connections.nim

@@ -0,0 +1,21 @@
+import std/strutils
+import ../src/allographer/connection
+
+let
+  maxConnections = 95
+  timeout = 30
+  mysqlUrl = "mysql://user:pass@mysql:3306/database"
+  mariadbUrl = "mariadb://user:pass@mariadb:3306/database"
+  pgUrl = "postgresql://user:pass@postgres:5432/database"
+
+  # rdb* = dbOpen(SQLite3, sqliteHost, maxConnections=maxConnections, shouldDisplayLog=false)
+  rdb* = dbOpen(SQLite3, ":memory:", maxConnections=maxConnections, shouldDisplayLog=false)
+  # rdb* = dbOpen(MySQL, mysqlUrl, maxConnections, timeout, shouldDisplayLog=true)
+  # rdb* = dbOpen(MariaDB, mariadbUrl, maxConnections, timeout, shouldDisplayLog=true)
+  # rdb* = dbOpen(PostgreSQL, pgUrl, maxConnections, timeout, shouldDisplayLog=true)
+
+template asyncBlock*(body:untyped) =
+  (proc(){.async.}=
+    body
+  )()
+  .waitFor()