feat: add vault support to Regex scanner for redacted value storage

[AnandShivansh]

Similar to the Anonymizer scanner, the Regex scanner now supports storing redacted values in a vault for later deanonymization. When a vault is provided, matched patterns are replaced with unique placeholders like [REDACTED_REGEX_1], [REDACTED_REGEX_2], etc., and the original values are stored in the vault.

Key changes:

• Add optional vault parameter to both input and output Regex scanners
• Store matched regex patterns in vault with unique indexed placeholders
• Maintain backward compatibility when no vault is provided (uses [REDACTED])
• Update llm_guard_api scanner configuration to pass vault to Regex scanners
• Implement proper counter management to avoid placeholder conflicts

Change Description

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Issue reference

This PR fixes issue #XX

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• [x] I have reviewed the contribution guidelines
• [x] My code includes unit tests
• [x] All unit tests and lint checks pass locally
• [x] My PR contains documentation updates / additions if required