fix: add system view fallback chain for Redshift schema discovery (#37)

On some Redshift clusters (data sharing, Lake Formation, Serverless),
svv_tables returns empty results. Add auto-detection at init time with
fallback chain: svv_tables -> svv_all_tables -> information_schema.

- Probe each source with COUNT query, pick first with rows > 0
- Handle column name differences (table_schema vs schema_name)
- Filter svv_all_tables by current_database() to avoid cross-DB noise
- Add db_filter to _get_table_columns for cross-DB isolation
- Extract _process_bulk_rows and _get_tables_bulk_information_schema
  to avoid state mutation in fallback (concurrency safe)
- Skip caching empty results to prevent 24h dead cache
- Normalize schema name to lowercase
- Add 8 unit tests for detection chain and row processing

Closes #37
Bump version to 0.2.0rc11.

Author: luiscarbonel1991

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "nlp2sql"
-version = "0.2.0rc10"
+version = "0.2.0rc11"
 description = "Enterprise-ready Natural Language to SQL converter with multi-provider support. Built for production scale (1000+ tables) with Clean Architecture."
 readme = "README.md"
 license = {text = "MIT"}

src/nlp2sql/__init__.py

@@ -20,7 +20,7 @@
 from .schema.example_store import ExampleStore
 from .services.query_service import QueryGenerationService
 
-__version__ = "0.2.0rc10"
+__version__ = "0.2.0rc11"
 __author__ = "Luis Carbonel"
 __email__ = "devhighlevel@gmail.com"