Allow log origin "proxy" (#4520)

With runtimeverification/haskell-backend#3974,
`kore-rpc-booster` increments execution depth and emits a rewrite trace
in the scenario of pruning all but one branches in a branching execute
response. The trace has origin `"proxy"`, because that's where the step
is effectively taken. This PR makes sure `pyk` is ready to handle this.

Co-authored-by: rv-jenkins <[email protected]>

Author: geo2a

pyk/src/pyk/kore/rpc.py

@@ -622,6 +622,7 @@ def to_dict(self) -> dict[str, Any]:
 class LogOrigin(str, Enum):
     KORE_RPC = 'kore-rpc'
     BOOSTER = 'booster'
+    PROXY = 'proxy'
     LLVM = 'llvm'