feat: add validateCronExpression

[Elessar1802]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

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• Test A
• Test B

Checklist

• The title of the PR states what changed and the related issues number (used for the release note).
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

[Copilot]

Pull Request Overview

This PR adds a new validateCronExpression function to validate cron expressions with basic syntax checking.

• Implements validation for standard 5-part cron expressions
• Supports common cron patterns including wildcards, ranges, step values, and comma-separated lists
• Returns validation results consistent with other validators in the file

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[AbhishekA1509]

Look into copilot comments once