fix(compiler): pass the ast to user-form in the arity error reporter

[skydread1]

Closes #79

• Pass the ast to user-form in the ::missing-instance-method-arity reporter, matching every other reporter in the namespace.
• Verified by dispatching the reporter directly: it now throws the diagnostic instead of an ArityException from user-form.
• Consumer smoke build under production flags rebuilt byte-identical smoke DLLs, so the emission path is unchanged.
• Paired refresh of magic.analyzer.errors.clj.dll and the dll-sources.edn record.