[sarankumar1325]

Fixes #861

LabelValues<T> uses T as a naked type parameter in its conditional, so TypeScript distributes it over a union of label names. For labelNames: ['a', 'b'] the type becomes Partial<Record<'a', ...>> | Partial<Record<'b', ...>>. Writes still compile, but reading labels back does not:

const { values } = await counter.get();
values[0].labels.a; // TS2339: Property 'a' does not exist on type ...

This wraps both sides of the conditional in a tuple ([T] extends [NoLabelNameType]), so the label names stay one object type with every key. The no-label case (T = never) now resolves to Partial<Record<string, never>> as intended, instead of never.

Tests:

• Added a case to test/typescript.ts that reads labels.a / labels.b from get() on a two-label counter, plus a @ts-expect-error for an undeclared label. tsc --project . fails on main with TS2339 and passes with this change.
• npm run lint, npm run check-prettier and jest (651 tests) pass.
• CHANGELOG entry under Unreleased.