Resolve models by configured table name

[nertzy]

Summary

• resolve loaded Active Record models by their configured table_name and connection pool
• preserve raw SQL extraction when no usable model exists, including id-less tables
• fail before writing fixtures when multiple unrelated models match one table
• cover relocated models, autoloaded models, STI, abstract ancestors, connection pools, schema errors, and custom serialization

Why

Fixture generation currently infers model constants from conventional table names. Rails applications can move a model to a different table with self.table_name, and those tables silently fall back to raw SQL. The fallback bypasses model-backed serialization and can emit database-native values instead of the fixture values Rails expects.