Implement binary expressions

[Seddryck]

Implement binary expression syntax for the existing Expressif operators |AND, |OR, and |XOR.

Use a dedicated CST node:

BinaryExpressionSyntax
├── left: ExpressionSyntax
├── operator: BinaryOperatorSyntax
└── right: ExpressionSyntax

Examples:

foo |AND bar
foo |OR bar
foo |XOR bar
!foo |AND bar

Requirements:

• preserve the concrete operator in the CST;
• reuse ordinary expression syntax for both operands;
• define and test associativity and precedence explicitly;
• ensure unary negation binds more tightly than binary operators;
• distinguish |AND, |OR, and |XOR from the ordinary | pipeline separator;
• keep semantic validation out of the parser.

Add corpus tests for each operator, chained expressions, unary/binary composition, whitespace, malformed operators, missing operands, and CST shape.