[Refactor] Refine AST to preserve JOIN and ORDER BY syntax + Unary operator support

[colinthebomb1]

Overview

This PR refines the AST to preserve syntactic distinctions that mo_sql_parsing treats as semantically different, ensuring faithful SQL roundtripping through the parser and formatter.

Code Changes

• Added JoinType.JOIN enum value to distinguish bare JOIN from explicit INNER JOIN (previously both mapped to JoinType.INNER)

• Changed OrderByItemNode default _sort from SortOrder.ASC to None to distinguish implicit ordering from explicit ORDER BY x ASC

• Updated parser to return JoinType.JOIN for bare JOIN and None sort for ORDER BY items without an explicit direction

• Updated formatter join type map to include JoinType.JOIN -> 'join' and JoinType.INNER -> 'inner join', and simplified ORDER BY logic to only emit sort when explicitly specified

• Updated expected ASTs in data/asts.py for queries 37 and 44 to match the new semantics

• Added UnaryOperatorNode as a dedicated node type for unary operators (e.g. NOT, unary -), and tightened OperatorNode so it always has a non-None left operand.

[Copilot]

Pull request overview

This PR refines the SQL AST so the parser/formatter can preserve syntactic distinctions needed for faithful SQL round-tripping (bare JOIN vs INNER JOIN, implicit vs explicit ORDER BY ... ASC) and introduces a dedicated unary-operator node.

Changes:

• Added JoinType.JOIN and updated parser/formatter to distinguish bare JOIN from INNER JOIN.
• Changed OrderByItemNode.sort default to None and updated parser/formatter to only emit sort direction when explicitly present.
• Added UnaryOperatorNode and updated parser/expected ASTs to represent unary operators (e.g., NOT, unary -) distinctly.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/test_query_parser.py	Adjusts parser test expectations for updated AST semantics (but currently disables a key assertion).
tests/test_ast.py	Updates AST unit tests to use UnaryOperatorNode.
data/asts.py	Updates expected ASTs (notably queries 37, 42, 44) to match new JOIN/ORDER BY/unary semantics.
core/query_parser.py	Updates JOIN type parsing, ORDER BY sort parsing, and unary operator parsing into UnaryOperatorNode.
core/query_formatter.py	Updates join-type emission, ORDER BY emission rules, and unary operator formatting.
core/ast/node.py	Tightens OperatorNode construction and introduces UnaryOperatorNode; makes ORDER BY sort optional.
core/ast/enums.py	Adds JoinType.JOIN.

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[colinthebomb1]

Unary operator LGTM!

[baiqiushi]

Thanks @colinthebomb1 !