Spatter Build Instructions and Intel Backend Fixes

[jyoung3131]

Overview

This PR adds some much needed improvements to Build.md. It also looks to fix the Intel OneAPI cmake package, which was using some hard-coded logic to find the OneAPI compiler.

Closes #252

✨ Change Description/Rationale

• Added details from build files to Build.md
• Removed some spurious lines in CMakeLists.txt
• Used Claude to fix/refactor the OneAPI cmake package file

If a longer explanation is required, it goes in paragraphs below the title sentence.

👀 Reviewer Checklist

• All GitHub actions and runners have passed if applicable
• Commits are clean and relevant

✅ PR Checklist

• Remove or update the template boilerplate text
• Commits are relevant and combined where appropriate
• Rebase off spatter-devel
• Reviewers Requested
• Projects associated
• Commits mention issue and/or PR numbers at the bottom of the message
• Relevant issues are linked into the PR
• TODOs are completed
• Reviewer checklist is updated

📌 Future Work

• Build.md may need additional updates as we clean up compiler support.