Add PostgreSQL PARTITION OF syntax support

[fmguerreiro]

Summary

This PR adds support for PostgreSQL's CREATE TABLE ... PARTITION OF syntax for creating child partition tables.

Closes #2042

Changes

• Added MODULUS and REMAINDER keywords to src/keywords.rs
• Added ForValues enum and PartitionBoundValue enum to src/ast/ddl.rs with Display implementations
• Added partition_of and for_values fields to CreateTable struct
• Updated CreateTableBuilder in src/ast/helpers/stmt_create_table.rs
• Added parser logic in src/parser/mod.rs for PARTITION OF, FOR VALUES IN/FROM/TO/WITH, and DEFAULT
• Updated src/ast/spans.rs to include new fields
• Exported new types from src/ast/mod.rs
• Added 7 comprehensive tests in tests/sqlparser_postgres.rs

Supported Syntax

-- RANGE partition
CREATE TABLE t PARTITION OF parent FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

-- RANGE with MINVALUE/MAXVALUE
CREATE TABLE t PARTITION OF parent FOR VALUES FROM (MINVALUE) TO ('2020-01-01');

-- LIST partition
CREATE TABLE t PARTITION OF parent FOR VALUES IN ('US', 'CA', 'MX');

-- HASH partition
CREATE TABLE t PARTITION OF parent FOR VALUES WITH (MODULUS 4, REMAINDER 0);

-- DEFAULT partition
CREATE TABLE t PARTITION OF parent DEFAULT;

-- Multi-column range
CREATE TABLE t PARTITION OF parent FOR VALUES FROM ('2023-01-01', 1) TO ('2023-04-01', 1);

-- With table constraints
CREATE TABLE t PARTITION OF parent (
    CONSTRAINT check_date CHECK (order_date >= '2023-01-01')
) FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

Testing

• All 7 new partition tests pass
• All 1312 existing tests pass (no regressions)
• cargo fmt passes
• Works with both PostgreSqlDialect and GenericDialect as required