refactor: extract buildNeedsAndStrategy helper function

[Mohamed-Elwasila]

Summary

• Extracted duplicate logic for building needs and strategy maps into buildNeedsAndStrategy() helper function
• Refactored NewExpressionEvaluatorWithEnv() and newStepExpressionEvaluator() to use the new helper
• Removed completed TODO comments about cleanup

Motivation

There was duplicate code (~20 lines) in two functions that built the same needs and strategy maps for expression evaluation. This refactoring improves maintainability and reduces the chance of inconsistencies.

Test Plan

• Code builds successfully (go build ./...)
• No linting errors (golangci-lint run)
• Code formatted with go fmt

Fixes TODO items in pkg/runner/expression.go:37 and pkg/runner/expression.go:124