Add support for optional arrow syntax: (2 ← 1) = (1 → 2) = (1 2)

[konard]

Summary

Implements issue #62 by adding support for optional arrow syntax in the Lino protocol.

• Right arrow syntax: (1 → 2) equals (1 2)
• Left arrow syntax: (2 ← 1) equals (1 2) (note the order reversal)
• Backward compatible: All existing syntax continues to work unchanged

Implementation Details

Grammar Changes

• C#: Updated Parser.peg with new arrowValues, rightArrowValues, and leftArrowValues rules
• JavaScript: Updated grammar.pegjs with equivalent arrow parsing rules
• Rust: Enhanced nom parser with arrow_values, right_arrow_values, and left_arrow_values functions

Syntax Examples

(1 2)       # Traditional syntax
(1 → 2)     # Right arrow - same result as above
(2 ← 1)     # Left arrow - same result as above (order reversed)
(papa → mama)   # Works with named references
(daughter ← papa) # Results in (papa daughter)

Version Updates

• C# version: 0.6.0 → 0.7.0
• JavaScript version: 0.6.0 → 0.7.0
• Rust version: 0.6.0 → 0.7.0

Test Coverage

Added comprehensive test suites across all implementations:

• C#: 4 new arrow syntax tests (all passing)
• JavaScript: 4 new arrow syntax tests (all passing)
• Rust: 4 new arrow syntax tests (all passing)

All existing tests continue to pass, ensuring full backward compatibility.

Test Results

C# Tests

Passed! - Failed: 0, Passed: 86, Skipped: 0, Total: 86

JavaScript Tests

84 pass, 0 fail, 211 expect() calls

Example Output

Input:  (2 ← 1)
Output: (1 2)

Input:  (1 → 2) 
Output: (1 2)

Input:  (1 2)
Output: (1 2)

🤖 Generated with Claude Code

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Resolves #62