Shiki's bundled JS/TS/JSX/TSX grammars carry a `template-call` rule whose
triple-nested lookahead sends the Oniguruma WASM engine into exponential
backtracking on ordinary backtick templates. The WASM heap grows until the
renderer runs out of memory and the window goes black.
Strip `template-call` from those four grammars as they are loaded in the
Shiki worker. Plain backticks and simple tagged templates still highlight;
only the rare `ident<TypeArgs>` tagged-template form loses its specialized
type-argument coloring.
Add a 5s per-request budget on the worker client as a safety net for any
other pathological pattern. Matching is synchronous inside the worker, so
the only way to reclaim its heap is to terminate it from the main thread.
A timed-out request resolves `null` like any other failure, so the caller
keeps plain text and nothing is written to the result cache.
Closes#2587
Bohdan Triapitsyn
b6e78fbed5