[abhinav-phi]

FOR NO KEY UPDATE and FOR KEY SHARE are valid PostgreSQL row locking strengths but were rejected:

sql parser error: Expected: one of UPDATE or SHARE, found: NO
sql parser error: Expected: one of UPDATE or SHARE, found: KEY

Add LockType::NoKeyUpdate / LockType::KeyShare, display them as NO KEY UPDATE / KEY SHARE, and parse them in parse_lock before the existing OF / NOWAIT / SKIP LOCKED handling.

Grammar: https://www.postgresql.org/docs/current/sql-select.html#SQL-FOR-UPDATE-SHARE

Tests cover both forms with OF and wait policies in PostgreSQL and Generic, and incomplete forms are rejected. Added fuzz seed fuzz/fuzz_seeds/postgres_2778_row_locking.sql.

Validation: cargo test --all-features, cargo fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings.

Fixes #2778.
AI-ASSISTED: yes. human reviewer: @abhinav-phi.

[slopgobblercobbler]

Audited the PostgreSQL row-locking strength extension in src/ast/query.rs and src/parser/mod.rs:

• AST representation and Display roundtrip:
  • Adding LockType::NoKeyUpdate and LockType::KeyShare accurately models PostgreSQL's row-level locking strengths (FOR NO KEY UPDATE and FOR KEY SHARE).
  • fmt::Display outputs "NO KEY UPDATE" and "KEY SHARE", integrating seamlessly with LockClause formatting (write!(f, "FOR {}", self.lock_type)) to achieve byte-exact roundtrip serialization.
• Parser lookahead and error reporting:
  • Lookahead sequencing in parse_lock checks NO -> [KEY, UPDATE] and KEY -> SHARE before falling back to [UPDATE, SHARE]. This prevents ambiguous keyword matching while providing precise diagnostics on truncated or mismatched clauses (e.g. FOR NO KEY SHARE rejecting on SHARE rather than failing generically).
  • Trailing clauses (OF, NOWAIT, SKIP LOCKED) execute after lock_type resolution, correctly supporting compositions such as FOR NO KEY UPDATE OF t SKIP LOCKED and FOR KEY SHARE OF t NOWAIT.
• Dialect behavior:
  • Both PostgreSQL and Generic dialects correctly accept the new clauses without altering syntax rules for other database engines.
• Test and fuzz coverage:
  • Unit tests comprehensively verify roundtrip formatting, AST structure (lock.of, lock.nonblock), and negative test cases for incomplete or invalid token sequences.
  • Adding fuzz/fuzz_seeds/postgres_2778_row_locking.sql ensures ongoing fuzzer validation.

Clean, idiomatic Rust AST contribution that closes a noticeable Postgres syntax gap with zero breaking changes.