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/.gitignore

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+*
+!*.*
+!*/
+!makefile
+
+# Created by https://www.gitignore.io/api/nim
+# Edit at https://www.gitignore.io/?templates=nim
+
+### Nim ###
+nimcache/
+
+# End of https://www.gitignore.io/api/nim
+
+!LICENSE
+!Dockerfile
+
+coverage
+lcov.info
+
+*.sqlite3
+*.srqlnb
+.migration.json
+*logs/*
+*.log
+.diff
+testresults
+
+
+gh-pages*
+.DS_Store
+pkg
+.vscode