fix(hclsyntax): implement recursion depth limit inside parseBinaryOps to prevent stack overflow

[PARTH-AI-DS20]

Summary

This PR introduces a hard recursion depth threshold of 1000 loops inside parseBinaryOps to safely intercept deeply nested expressions (such as thousands of sequential parenthetical configurations) before they exhaust the standard Go goroutine stack runtime allocation.

Root Cause & Resolution

• The Bug: When parsing configurations with excessive nested layers like (((((...))))), the recursive descent structure of parseBinaryOps continually allocates frames on the stack. This eventually results in a non-recoverable, fatal stack overflow panic (runtime: goroutine stack exceeds 1000000000-byte limit).
• The Fix: Added a tracking field recursionDepth to the internal package parser struct. Entering parseBinaryOps increments this counter, checks against a strict max ceiling (1000), and returns a structured hcl.Diagnostic payload gracefully if crossed instead of throwing an unhandled panic. It clears down via a deferred frame decrement step.
• Testing: Implemented a target validation regression block TestParseExpression_nestedParenthesesRecursionGuard inside parser_test.go to assert defensive validation engine boundaries.

Fixes #809

[hashicorp-cla-app]

All committers have signed the CLA.