fix: route v2 callables through wrapV2 when platform is gcfv2

[IzaakGough]

Fixes #310.

With firebase-functions 7, wrap() treated v2 onCall functions as v1 callables, so the handler received no auth or other request fields.

This routes v2 callables to wrapV2 based on the function's trigger metadata instead of its parameter count.

• The platform check is required. v1 callables also carry callable trigger metadata, so only functions marked gcfv2 take the v2 path.

Tested with unit tests for v2 callables, v2 onRequest and v1 callables, and against this MRE.

[gemini-code-assist]

Code Review

This pull request introduces support for identifying and wrapping GCFv2 callable functions by checking the platform field in the endpoint metadata. Key changes include exporting the isCallableV2Function utility, updating the wrap function to prioritize v2 callable detection, and adding a corresponding test case in spec/main.spec.ts to ensure correct routing. There are no review comments to address, and I have no further feedback to provide.

[cabljac]

This looks great. The __endpoint.platform === 'gcfv2' check is a much more stable signal than counting function parameters, and the regression test covers the routing path nicely. A couple of small questions below, neither blocking.

[cabljac]

The callable fix itself looks right to me: platform check first with the arity heuristic as fallback is the correct order, and the v1-callable negative test plus the realistic rest-param shape in the regression test address everything from my last review. Ran this against both firebase-functions 4.9.0 and 7.2.5 and the routing behaves. One behavioral concern inline before this goes in, plus a couple of smaller ones.

[cabljac]

LGTM with comments