chore: gax linter fixes

[shivanee-p]

Resolves legacy ESLint promise violations in core/packages/gax/test/unit/grpc.ts and grpc-fallback.ts

• Wrapped callback-based RPC calls in Promise constructs
• added async() + await callbacks

[gemini-code-assist]

Code Review

This pull request introduces telemetry tracing configuration generation in the GAPIC generator for TypeScript (supporting both CJS and ESM templates) and updates the google-gax library to accept and propagate enableTelemetryTracing and internalTelemetryInfo parameters. Additionally, it modernizes several unit tests to use async/await instead of callbacks or promise chains. The review feedback highlights opportunities to avoid variable shadowing in the fallback tests by renaming caught error variables, and to simplify assert.rejects calls in the gRPC tests by passing promises directly instead of wrapping them in unnecessary async arrow functions.

[danieljbruce]

LGTM. The async tests are cleaner to read too!