fix(core): recurse variable substitution into nested dicts and lists

[Ankit-cs]

Related to #296

Pull Request Template

Description

• What changes are being made?

  • Updated _replace_vars_in_dict and added _replace_vars_in_list in src/tirith/core/policy_parameterization.py to recursively substitute variables across nested dictionaries and lists.
  • Added unit tests in tests/core/test_policy_parameterization.py covering nested dict and list variable substitution as well as reporting of missing variables in nested structures.

• Why are these changes necessary?

  • Previously, _replace_vars_in_dict only walked top-level keys and skipped non-string values. Nested placeholders like {{var.x}} inside condition.value were never substituted and reached evaluators as literal strings while leaving not_found_vars empty.

• Which issues or tickets does this PR close or relate to?

  • Closes fix(core): variable substitution does not recurse — nested {{var.x}} silently produces wrong verdicts #296
  • Related issue: fix(core): variable substitution does not recurse — nested {{var.x}} silently produces wrong verdicts #296

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Code has been linted.
• Documentation has been updated (if needed).
• Tests have been added and verified (100% passing).

[Ankit-cs]

looking for feedback @refeed

[codecov]

Codecov Report

❌ Patch coverage is 86.36364% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/tirith/core/policy_parameterization.py	86.36%	2 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
src/tirith/core/policy_parameterization.py	94.33% <86.36%> (-5.67%)	⬇️

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