fix: user attributes missing when calling execute call

[Mansi-mParticle]

Instructions

1. PR target branch should be against development
2. PR title name should follow this format: https://github.com/mParticle/mparticle-workflows/blob/main/.github/workflows/pr-title-check.yml
3. PR branch prefix should follow this format: https://github.com/mParticle/mparticle-workflows/blob/main/.github/workflows/pr-branch-check-name.yml

Summary

• Previously, when fetching user attributes from the current user, the latest attributes were not always retrieved because they were not yet ready at the time of access.
  This PR fixes that by combining the current user’s attributes with the attributes passed in by the user in select placement. If the current user attributes include newer values, they will override the existing ones. This ensures that we always send the most complete and up-to-date set of attributes to the selected placement.

Testing Plan

• Was this tested locally? If not, explain why.
• Tested with sample app and executed test case.

Reference Issue (For mParticle employees only. Ignore if you are an outside contributor)

• Closes https://go.mparticle.com/work/SDKE-380