Ignore stale initial links after reconfiguration

[OskarEichler]

Problem

Reconfiguring deep linking removes the previous URL-event listener, but it cannot cancel that configuration's pending getInitialURL() promise. If the old promise resolves later, its URL is handled through the new configuration and can be duplicated, misrouted, or sent to the wrong callback. A rejected initial-URL lookup can also escape as an unhandled rejection.

Fix

• generation-tag each linking subscription
• invalidate the generation during teardown
• ignore initial URLs resolved by stale configurations
• absorb initial-URL lookup failures while keeping the live URL listener operational

Breaking changes

None. Only stale or failed initial-URL lookups change behavior; current subscriptions and live URL events are unchanged.

Test plan

• Added a deferred-promise regression proving an old configuration's initial URL reaches neither old nor new callbacks.
• Added rejection coverage proving later live URL events still process exactly once.
• Focused suite passes: 30/30 tests.
• Full yarn test-js passes: 38 suites/397 tests; 11 suites/59 tests remain intentionally skipped.
• Focused ESLint, Bob module/type builds, and git diff --check pass.