feat(pgwire): support struct type in extended mode

[fuyufjh]

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What's changed and what's your intention?

Closes #7949.

sqllogictest-rs doesn't support struct type yet, so I added a Python test in e2e-test.

References:

• Postgres code src/backend/utils/adt/rowtypes.c
• Pseudo-type of struct & array of struct: src/include/catalog/pg_type.dat

Checklist

• [ ] I have written necessary rustdoc comments
• [ ] I have added necessary unit tests and integration tests
• [ ] I have added test labels as necessary. See details.
• [ ] I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features #7934).
• [ ] My PR contains breaking changes. (If it deprecates some features, please create a tracking issue to remove them in the future).
• [ ] All checks passed in ./risedev check (or alias, ./risedev c)
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Documentation

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Release note

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