fix: enforce maximum expression length in MathParser

[myarichuk]

🎯 What: Enforced a maximum length (100,000 characters) for mathematical expressions in ArenaMathParser.Tokenize.

⚠️ Risk: Potential Denial of Service (DoS) via unbounded memory allocation if a malicious user provides an extremely large input string that the parser attempts to tokenize into the arena.

🛡️ Solution: Added a MaxExpressionLength constant and a check at the beginning of the Tokenize method to throw a SyntaxErrorException if the input length exceeds this limit. This prevents any allocations for excessively large, malicious payloads. Also added a new test project tests/SimpleMathParser.Tests with test cases to verify the enforcement of this limit.

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PR created automatically by Jules for task 7111314682171355679 started by @myarichuk

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