Refactor version resolution logic into helper functions (#2)

Summary

Refactor the action script by moving the version resolution workflow out of scripts/main.ps1 and into a dedicated scripts/Helpers.psm1 module.

This keeps main.ps1 as a thin orchestrator and makes the individual steps easier to read, compare, and validate.

Changes

• extract action input parsing into Read-ActionInput
• extract publish settings parsing into Get-PublishConfiguration
• extract pull request event loading into Get-GitHubPullRequest
• extract release decision logic into Resolve-ReleaseDecision
• extract GitHub and PowerShell Gallery version lookups into dedicated helpers
• extract next-version calculation and action output writing into dedicated helpers
• update scripts/main.ps1 to orchestrate the helper calls

Notes

• Intended behavior is unchanged for the normal release/version resolution path.
• Error handling now throws from helper functions instead of using inline Write-Error/exit in main.ps1.

Validation

• verified the refactor against main with git diff --function-context
• verified both edited PowerShell files report no editor errors locally