Add cursor pagination to fetchTipEvents

[Abioladory123]

Summary

fetchTipEvents takes a startLedger and a limit and returns whatever fits.
There is no cursor, so a caller that receives a full page has no way to ask for
the next one except by guessing a new start ledger, which risks either skipping
events or reprocessing them.

The RPC returns paging information the function currently discards.

Acceptance criteria

• The function accepts a cursor and returns one for the next page when more
  events are available.
• Paging through a range yields every event exactly once.
• The paging contract is documented with an example loop in the README.

Getting started

Fork this repository, clone your fork, and add this repo as upstream:

git clone https://github.com/<your-username>/novatip-sdk.git
cd novatip-sdk
git remote add upstream https://github.com/Novatip/novatip-sdk.git
npm install

Create a branch for this issue:

git checkout -b feat/events-pagination

Suggested commit message:

feat: support paging through tip events

Run npm run lint, npm run typecheck, and npm run build before pushing, then open a pull request from your fork against main and link this issue. See the contributing guide for the full workflow.