Migrate IP address inference to `dataCollection.userInfo`

Replace `sendDefaultPii` checks for IP address handling with `dataCollection.userInfo`.

## Callsites

1. `client.ts:63` — `infer_ip` setting for Relay: `options.sendDefaultPii ? 'auto' : 'never'`
2. `client.ts:85` — `addAutoIpAddressToSession` listener gated on `sendDefaultPii === true`

Both should read from the resolved `dataCollection.userInfo` instead.

## References

* `packages/core/src/js/client.ts`
* `packages/core/test/client.test.ts` — existing tests for IP address behavior

Start in packages/core/src/js/client.ts at lines 63 and 85, then review the existing IP address tests in packages/core/test/client.test.ts. Update both callsites to use the resolved dataCollection.userInfo value and adjust or add tests confirming the Relay setting and session listener behavior.

Written by the indexing model from the issue text.