fix: correct wire protocol type OIDs for pre-existing SQLite tables (#68)

[erans]

Summary

• Add sqlite_type_to_pg_type_name helper to map SQLite declared types to PostgreSQL type name strings
• Add get_column_types_from_pragma method to DbHandler that uses PRAGMA table_info as a fallback for tables without __pgsqlite_schema metadata
• Add PRAGMA type fallback in simple query protocol (executor.rs) and extended query protocol (extended.rs) — covering Parse-time schema_types, Execute-time schema_types, and Parse-time inferred_types paths
• Skip empty and default-text PRAGMA types to preserve value-based inference for untyped/virtual table columns

Fixes #68 — integer, bigint, smallint, boolean, and float columns in pre-existing SQLite tables now report correct OIDs instead of always returning OID 25 (TEXT).

Test plan

• All 487 unit tests pass
• All integration tests pass (datetime, pg_index, etc.)
• cargo check — no errors
• cargo clippy — no new warnings in changed files
• Verify with psycopg3 binary protocol that pre-existing SQLite tables return correct type OIDs

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