Feature/using join

[stefanoperenzoni]

Description

This PR implements the USING clause syntax for joins in Malloy. 90% agent generated.

Previously, users were forced to use the with or on keywords to define join conditions (e.g., join_one: aircraft_models on aircraft_model_code = aircraft_models.aircraft_model_code). With this change, users can succinctly join tables sharing the same column names using the SQL standard USING syntax.

Syntax supported:
```malloy
source: aircraft extend {
join_one: aircraft_models using (aircraft_model_code)
}

run: table1 extend {
join_one: table2 using (id, code)
} -> { select: id, code, val1, table2.val2 }
```

What this PR does

• Parser Updates: Added USING rules to MalloyLexer.g4 and MalloyParser.g4.
• AST/IR: Created a UsingJoin node (join.ts) which generates an internal equivalence relation so that Malloy's semantic engine understands the lineage of the fields.
• SQL Generation:
  • Modified query_query.ts to output valid USING (col1, col2) SQL.
  • Added logic to automatically push extra join filters (where: conditions on the joined source) into a subquery, preventing invalid SQL since AND cannot be appended to a USING clause.
• Alias Prefix Stripping: Updated field_instance.ts to automatically strip table aliases from columns involved in an active USING join. Because dialects like BigQuery coalesce USING columns, fully qualifying them (e.g. base_table.id) results in query failures.
• Testing: Added thorough integration tests in join.spec.ts to cover single-column joins, multi-column joins, source-level refinements, and inline query joins.

Related Issues

Resolves #2541

Checklist

• Code compiles correctly
• Linter (npm run lint) passes
• Tests (npm run test) pass
• Developer Certificate of Origin (DCO) sign-off is included