Fix #1029: correct left-associativity for arithmetic operators

[facontidavide]

Summary

• Fix left-to-right associativity for +, -, *, / operators in the script parser
• A - B + C was incorrectly evaluated as A - (B + C) due to conflicting binding power levels in lexy's operation list
• Adds regression tests for arithmetic associativity

Test plan

• New test: ScriptParser.Associativity_Issue1029
• All existing tests pass (298/298)

Closes #1029

Summary by CodeRabbit

• Bug Fixes

  • Fixed operator associativity handling in scripting, resolving precedence conflicts with string concatenation and arithmetic operations.

• Tests

  • Added test suite validating left-associativity for arithmetic and string operations (Issue1029).

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[coderabbitai]

Caution

Review failed

The pull request is closed.

📝 Walkthrough

Walkthrough

A targeted fix to the scripting operator grammar where string_concat's operand type is changed from math_sum to math_prefix to correct left-associativity behavior in arithmetic expressions, accompanied by test coverage validating operator precedence and associativity.

Changes

Cohort / File(s)	Summary
Operator Grammar Fix include/behaviortree_cpp/scripting/operators.hpp	Changed operand type in string_concat struct from math_sum to math_prefix to correct associativity binding chain and resolve operator precedence conflicts.
Operator Associativity Tests tests/script_parser_test.cpp	Added comprehensive test case OperatorAssociativity_Issue1029 with assertions validating left-associativity for arithmetic operations (addition/subtraction, multiplication/division), mixed precedence evaluation, and string concatenation behavior.

Estimated Code Review Effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 Hops of joy, the order's right!
No more math that gives a fright,
A minus B plus C now flows,
Associativity clearly shows,
Grammar fixed with one small change ✨

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/issue-1029

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