[osipovartem]

Summary

Backport the namespace portion of Apache sqlparser #2767 to the parser revision actually used by Rustice.

• Add a native DescribeObject AST for DESC/DESCRIBE DATABASE and SCHEMA, preserving aliases, quoted identifier boundaries, Display, serde and visitors.
• Preserve this fork's existing DESCRIBE VIEW AST (ExplainTable::has_view_keyword) and existing TABLE/STAGE/FILE FORMAT/SEQUENCE/WAREHOUSE paths.
• Dispatch namespace statements before EXPLAIN query modifiers: reject forms such as DESC ANALYZE DATABASE d instead of silently losing ANALYZE.
• Namespace names are not table relations in visitors.
• Apply small behavior-preserving current-toolchain lint corrections needed for strict all-target/all-feature Clippy.

This PR deliberately targets oracle/qualify-table-comment-null-20261107, the current Rustice parser base, rather than the diverged default branch. Original author and cherry-pick provenance are retained. Runtime support belongs in Rustice; this parser PR alone does not enable execution.

Validation

• Complete offline all-features suite: 1,590 passed, 7 ignored, zero failures (including 47 doctests).
• Strict cargo clippy --all-targets --all-features -- -D warnings: passed.
• Serde-only common-test compilation without the optional serde_json feature: passed; one pre-existing irrefutable-pattern warning remains in this non-all-features configuration.
• cargo fmt --all -- --check and git diff --check: passed.
• Regression tests reproduced the legacy VIEW AST break and swallowed query modifiers before the fixes.
• Independent read-only agent review: approved, no remaining blockers; reviewed diff SHA-256 e3d94375ef7fd87b084aed2302d399ac2f0f8625646a4c8ef29c9bb1db3331e9.

Uses a shared existing target directory; no full DataFusion rebuild or new Snowflake query was needed for parser qualification.