Integrate SQLGlot for SQL to Pure Relation conversion

[neema2]

This PR integrates SQLGlot into the legendql branch to enable conversion of SQL statements into Pure "Relation" code.

Changes

• Added SQLGlot dependency for SQL parsing
• Created SQLParser class that converts SQLGlot AST to LegendQL metamodel
• Added Query.from_sql() method for creating queries from SQL
• Added from_sql() function to the LegendQL API
• Added comprehensive test suite for SQL parsing
• Updated tests to assert against correct Legend Pure code format

Example Usage

import legendql as lq
from legendql.model.schema import Table, Database
import pyarrow as pa

# Create table and database
table = Table("tableC", [pa.field("colA", pa.utf8()), pa.field("colB", pa.utf8())])
database = Database("test::Database", [table])

# Parse SQL and generate Pure Relation code
sql = "select colA, colB from tableC"
query = lq.from_sql(sql, database)
pure_relation = query.to_string()
# Output: #>{test::Database.tableC}#->select(~[colA, colB])->from(legendql::Runtime)

Testing

• Added unit tests for SQL parser functionality
• Verified integration with existing LegendQL API
• Tested with the example from the task: "select colA, colB from tableC"
• Updated test assertions to verify exact Pure relation code format
• All 29 tests pass successfully

Pure Relation Code Format

The SQL parser generates correct Pure relation syntax:

• Basic SELECT: #>{database.table}#->select(~[col1, col2])->from(legendql::Runtime)
• WHERE clauses: ->filter(column==value)
• ORDER BY: ->sort([~column->ascending(), ~column->descending()])
• LIMIT: ->limit(number)
• OFFSET: ->drop(number)

Fixes the requirement to convert SQL statements into Pure "Relation" code using SQLGlot's AST parsing capabilities.

Link to Devin run: https://app.devin.ai/sessions/c47cbf6679c54bb98ab35459c946bf98

Requested by: neema.raphael@gs.com

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