fix(fsharp): propagate DerivedVariable IsReferenced to same-named Arguments - #563

…uments

WriteFSharpMethod prefixes unreferenced method arguments with `_` to
satisfy
the F# compiler's unused-variable warnings. The check used
arg.IsReferenced,
but a method argument and a DerivedVariable that aliases the same name
are
distinct Variable instances — so marking one referenced had no effect on
the
other.

Concrete case: Wolverine's HandlerChain adds ContextVariable("context",
IMessageContext) to DerivedVariables so middleware can resolve
IMessageContext.
When a middleware frame resolves that alias and marks it referenced, the
actual
HandleAsync argument (`context: MessageContext`) stayed IsReferenced =
false.
WriteFSharpMethod then emitted `_context` in the signature while the
generated
body still used `context`, producing FS0039 ("value or constructor
'context' is
not defined") on every handler that had IMessageContext-consuming
middleware.

Fix: before building the argument list in WriteFSharpMethod, walk
Arguments and
set IsReferenced = true on any whose Usage matches a referenced
DerivedVariable.
Setting it on the Variable object itself (inside the JasperFx assembly,
so
`internal set` is reachable) keeps all downstream codegen — including
frames
that read arg.IsReferenced directly — consistent with the updated state.