Context should not use async

[BrynCooke]

Currently Context contains an async datastructure.

This has the following downsides:

• Eq/PartialEq cannot be derived.
• map_request and map_response can't store or retrieve in context as they are non async.
• Scripting plugins/Deno/WASM can't store or retrieve in context as they are non async.

Possible alternatives:

• Merge strategy - All contexts are merged on the way back and if there are non-unique results then they are discarded.
• Synchronous lock - Should not have much contention, maybe this is OK? Doesn't work.

[o0Ignition0o]

What’s our merge strategy ?
Prevent async / locking mechanisms

Maybe we shouldn’t provide Arc<Mutex<>> but require Send + Sync

Maybe adding convenience wrappers would suffice for now