fix: add Snowflake dialect to SQL parser

[atvaccaro]

Summary

• Fix Snowflake SQL statement type detection by adding dialect="snowflake" to sqlglot parser
• Fixes issue COPY statements incorrectly classified as "Unknown" instead of "Copy" Snowflake-Labs/mcp#161: COPY statements and other Snowflake-specific syntax now correctly identified
• Add comprehensive test suite (35 tests) covering basic SQL and Snowflake JSON/variant syntax
• Enable pytest in CI pipeline

Test Results

Statements that work both with and without dialect (baseline)

SQL	Result
SELECT * FROM my_table	Select ✓
INSERT INTO my_table VALUES (1, 2)	Insert ✓
COPY INTO my_table FROM @my_stage	Copy ✓
SELECT data:name FROM my_table	Select ✓

Statements FIXED by adding dialect="snowflake"

SQL	Without dialect	With dialect
SELECT data:user.address.city FROM t	ParseError → Unknown	Select ✓
SELECT data:count::INTEGER FROM t	ParseError → Unknown	Select ✓
SELECT f.value FROM t, LATERAL FLATTEN(input => data:items) f	ParseError → Unknown	Select ✓
COPY INTO t FROM @stage PATTERN='*.csv' FILE_FORMAT=(...)	ParseError → Unknown	Copy ✓
COPY INTO @stage FROM t FILE_FORMAT=(TYPE='PARQUET')	ParseError → Unknown	Copy ✓
SELECT data:items[0]:name FROM t	ParseError → Unknown	Select ✓
SELECT * FROM t WHERE data:status::STRING = 'active'	ParseError → Unknown	Select ✓
SELECT ARRAY_SIZE(data:items) FROM t	ParseError → Unknown	Select ✓
PUT file:///tmp/data.csv @my_stage	ParseError → Unknown	Command ✓

Test Plan

• All 44 tests pass (35 new + 9 existing)
• Verified parsing of COPY, JSON paths, VARIANT casts, and Snowflake-specific functions
• 9 SQL patterns now correctly parse with the fix that would have failed before

🤖 Generated with Claude Code

[darinim-notion]

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