Add event fetching for jar creation

[Abioladory123]

Summary

The contract deliberately has no on-chain list of jars. Discovery is
event-driven: create_jar emits jar_crtd, and indexers are expected to
reconstruct the jar list by scanning those events. The SDK only fetches tip
events, so it offers no way to do the thing the contract's design assumes.

Anything wanting to enumerate jars has to build its own filter and decoder,
which is exactly the encoding work this package already solved once for tips.

Acceptance criteria

• A function fetches and decodes jar_crtd events into a typed result
  carrying the jar id, owner, ledger and transaction hash.
• It reuses the existing topic filter construction rather than duplicating
  the XDR encoding.
• The function is exported from the package entry point and documented.

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/fetch-jar-created-events

Suggested commit message:

feat: fetch and decode jar_crtd 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.