Resolve #2873: Remove runtime test port reservation race

[ayden94]

Summary

Remove the reserve-close-rebind race from the runtime in-flight shutdown network test by letting the application bind an OS-assigned port directly.

Linked context: #2873

Closes #2873

Changes

• Configure the cited Node runtime test with port: 0 instead of reserving and releasing a port first.
• Resolve the bound NodeHttpApplicationAdapter after listen() and read the actual server address for the test request.
• Release the blocked response and close the application in finally so assertion failures cannot leave shutdown waiting indefinitely.
• Keep the shared reservation helper and its unrelated call sites unchanged.

Testing

• Focused in-flight shutdown test: 1 passed.
• Repeated focused flake check: 20/20 passed.
• pnpm --filter @fluojs/runtime typecheck - passed.
• pnpm --filter @fluojs/runtime test - 29 files, 311 tests passed.
• Biome check - passed.
• LSP diagnostics - no errors or warnings; only pre-existing deprecation hints in the test file.
• git diff --check HEAD^..HEAD - passed.

Release impact

• This PR has consumer-visible release impact and includes a changeset.
• This PR has no consumer-visible release impact.

No Changeset is required because this changes only test setup and cleanup; published runtime behavior, API surface, and package contents are unchanged.

Public export documentation

• Not applicable: no public exports or source documentation changed.

Behavioral contract

• No documented behavioral contract changed.
• The existing in-flight shutdown assertion remains intact while its network setup is made race-free.
• Production runtime source is unchanged.

Platform consistency governance (SSOT)

• Not applicable: no platform contract, adapter implementation, governance document, or conformance claim changed.