Implement $call output handling and $try semantics

[ikskuh]

Motivation

• Make $call behave like $yield by supporting optional $try error propagation and optional -> $state / -> ${state} output assignment so procedure return values are consumed by callers.
• Ensure caller-side consumption of procedure return storage (sm.data.<Proc>) happens exactly once and that invalid usages (e.g. capturing from void or unknown state) produce compiler errors.

Description

• Extended IR Call to include output_variable: ?[]const u8 and use_try: bool and updated dumper output to show these flags.
• Updated CodeGen lowering to validate call targets, determine whether $try should apply (only when procedure returns an error union), detect void returns and reject -> usage, resolve -> $state vs -> ${out} targets, create state variables when needed, and emit .call instructions carrying the new fields.
• Added helpers parse_state_reference, is_void_type, and error_union_payload to parse/validate output targets and return types during lowering.
• Updated the Renderer to emit code after a CALL hopstate that consumes the callee's return storage by optionally performing try on sm.data.<Proc> and assigning the result into the requested output state (or discarding with _ = try ... when no output was requested), and preserved the runtime recursion guard and branch/resume behavior.
• Adjusted generation of the Data struct so scoped state entries keep their error-union payload type where needed to allow correct try emission for $call $try.
• Added examples/call_output.zigsm containing tests for new behaviors and registered it in build.zig.

Testing

• Ran the project test suite with zig build test which compiled the generated example code and executed the example unit tests; the build and tests completed successfully.

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Codex Task