Fix PostgreSQL regex check import

[yzxcj797]

Summary

• normalize the text cast that pgAdmin emits after regex CHECK patterns before PostgreSQL SQL parsing
• keep casts outside CHECK expressions and text inside regex literals unchanged
• add a regression test and run it in the Node 20/22 build matrix

Validation

• npm test (2 tests)
• npm run lint
• npm run build
• git diff --check

Fixes #242

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