feat(snowflake)!: Type annotation for Snowflake LOCALTIMESTAMP

[fivetran-kwoodbeck]

Maps Snowflake's LOCALTIMESTAMP() to CurrentTimestamp, similar to other timestamp aliases (GETDATE, SYSTIMESTAMP).

Documentation:
https://docs.snowflake.com/en/sql-reference/functions/localtimestamp

Changes:

• snowflake.py: Add LOCALTIMESTAMP → CurrentTimestamp in FUNCTIONS
• typing/snowflake.py: Add type annotations for CurrentTimestamp and Localtimestamp returning TIMESTAMPLTZ
• test_dialect.py: Exclude Snowflake from LOCALTIMESTAMP(n) read tests (can't roundtrip due to alias, test included instead in test_snowflake.py)
• test_snowflake.py: Add identity tests for LOCALTIMESTAMP() and LOCALTIMESTAMP(3)
• annotate_functions.sql: Add type annotation tests

[github-actions]

SQLGlot Integration Test Results

Comparing:

• this branch (sqlglot:feature/annotatetype-localtimestamp, sqlglot version: feature/annotatetype-localtimestamp)
• baseline (main, sqlglot version: 28.5.1.dev54)

⚠️ Limited to dialects: snowflake

By Dialect

dialect	main	sqlglot:feature/annotatetype-localtimestamp	difference	links
snowflake -> duckdb	626/1085 passed (57.7%)	626/1085 passed (57.7%)	No change	full result / delta
snowflake -> snowflake	981/1085 passed (90.4%)	981/1085 passed (90.4%)	No change	full result / delta

Overall

main: 2170 total, 1607 passed (pass rate: 74.1%), sqlglot version: 28.5.1.dev54

sqlglot:feature/annotatetype-localtimestamp: 2170 total, 1607 passed (pass rate: 74.1%), sqlglot version: feature/annotatetype-localtimestamp

Difference: No change