fix(pg-catalog): ignore extra cast fields

[discord9]

Summary

• Ignore additional fields in Expr::Cast pattern matches inside RewriteRegclassCastToSubquery.
• Matches the compatible pattern style already used by the published datafusion-pg-catalog 0.15.1 crate.
• Allows GreptimeDB, which patches sqlparser with an extra array field on Expr::Cast, to compile against the fork after fix(pg-catalog): restrict unqualified pg table rewrite #1.

Tests

• cargo test --manifest-path datafusion-pg-catalog/Cargo.toml --lib