Parser-only second step of the error-handling stream. No sema/codegen.
- token: 4 keywords — `raise`, `try`, `catch`, `onfail`.
- ast: RaiseStmt, TryExpr, CatchExpr {operand, binding?, body, is_match_body},
OnFailStmt {binding?, body}.
- parser:
- `try` is a unary prefix (binds tighter than `or`; right-recursive so it
stacks under `xx`/`@`/etc).
- `or` is already left-associative (precedence-climbing loop) — no change.
- `catch` is a postfix with four body shapes (no-binding block / block /
bare-expr / `== { case }` match-body, the latter reusing parseMatchBody
with the binding as subject).
- `raise EXPR;` and `onfail [e] { } | onfail EXPR;` statements; `error`
parses in expression position so `raise error.X` works; raise rejected
in expression position and inside an onfail body (in_onfail_body flag).
- consumer-aware `|>`: pipes the LHS into the head call through a
try/catch/or wrapper, preserving the wrapper.
- print: printExpr + match-arm printing for round-trips (anyerror!void to
break the printExpr<->printMatchArms inferred-error-set loop).
- sema/lsp: exhaustive switch arms for the 4 nodes + 4 keyword tokens.
- tests: ~22 inline parser tests (precedence, all catch forms, both
rejections, pipe cases, round-trip prints incl. match-body).
zig build, zig build test (264), and 254/254 examples green.
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