Fully replace ThreadLocal in Request with CHM

[SirYwell]

Overview

Description

I've seen multiple Spark profiles now where the ThreadLocal lookups added significant overhead. We don't actually need it because we already maintain a ConcurrentHashMap with the same information.

Submitter Checklist

• Make sure you are opening from a topic branch (/feature/fix/docs/ branch (right side)) and not your main branch.
• Ensure that the pull request title represents the desired changelog entry.
• New public fields and methods are annotated with @since TODO.
• I read and followed the contribution guidelines.