Parse Snowflake structured ARRAY types

[osipovartem]

Summary

• parse Snowflake ARRAY(element_type) syntax in casts and column definitions
• preserve existing untyped ARRAY behavior
• cover both structured and semi-structured forms in Snowflake parser tests

Validation

• cargo +1.95.0 test --test sqlparser_snowflake (162/162)
• cargo +1.95.0 clippy --all-targets -- -D warnings
• cargo +1.95.0 fmt --all -- --check