Fixes #214.

Root cause

The emsdk toolchain update in #203 (shipped in 2.2.0) regressed the wasm memory declaration. The old fastcomp build emitted growable memory (min 1 page, no maximum), but the upstream emscripten build defaults to fixed-size memory:

With maximum == initial, the unconditional memory.grow() in parse() throws WebAssembly.Memory.grow(): Maximum memory size exceeded for any source that doesn't fit the initial 16 MiB. Since the source is copied in as UTF-16 (4 * (len + 1) bytes), that's the ~4M char threshold reported in the issue. The asm.js build was unaffected.

Fix

Add -s ALLOW_MEMORY_GROWTH=1 to the emcc build, restoring growable memory (max 32768 pages / 2 GiB, emscripten's default ceiling — ~512M chars of source).

The issue repro now passes against the rebuilt dist/lexer.js:

import { parse, init } from 'es-module-lexer';
await init;
const big = 'const x = "' + 'a'.repeat(5 * 1024 * 1024) + '";\n';
parse(big); // OK (previously threw)

Also adds a 5MB large-source regression test, verified to fail against a fresh build off main and pass with this change; chomp test passes (149 tests, wasm + asm).