fix: use factory method to create policy eval functions

[paullatzelsperger]

• use ParticipantAgentPolicyContext
• use single factory method

What this PR changes/adds

use static factory methods to instantiate policy evaluation functions.

Why it does that

with the advent of the ParticipantAgentPolicyContext this became possible to simplify things

Further notes

List other areas of code that have changed but are not necessarily linked to the main feature. This could be method signature changes, package declarations, bugs that were encountered and were fixed inline, etc.

Linked Issue(s)

Closes # <-- insert Issue number if one exists

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