Replace tap with the built-in node:test runner

[szegedi]

Why

The recent tap bump (#49) surfaced that tap — via @tapjs/processinfo — pulls in uuid@14, whose node build references the global crypto. That global is unavailable unflagged on Node 18 and is unreliable inside processinfo's ESM loader hook, which broke CI. Rather than work around a heavyweight test-runner dependency, this drops tap entirely in favor of Node's built-in test runner.

What

• Rewrite src/index.test.ts against node:test + node:assert. tap's loose assertions map directly:

  • t.equal → assert.strictEqual
  • t.same → assert.deepEqual (loose — needed for the protobufjs-compat test, which compares bigint/number against the string longs that toObject({longs: String}) produces)
  • t.has → a small recursive loose-subset helper (assertHas)

  The constructs/encodes/decodes tap plugin became plain functions taking the test context.

• Compile tests with tsc (tsconfig.test.json) to dist-test/ and run them with node --test, so they work on every supported Node version — including 18, which can't strip types natively.

• Fix testing/proto/package.json {"module":"commonjs"} → {"type":"commonjs"} so the generated CJS protobuf module resolves under Node's native ESM loader. (The old value was a no-op that only worked because tap's loader bypassed native resolution.)

• Drop the tap dependency and its config block.

• Re-add Node 18 and add Node 26 to the test matrix (now [18, 20, 22, 24, 26]).

Verification

npm test and npm run lint pass locally. The compiled tests were run on Node 18, 20, 22, 24, and 26 — 72/72 passing on every version. A negative check (corrupting one expected encoding) fails correctly with exit 1.

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