fix: handle json format

[julien-deramond]

Description

This PR tries to fix #98 based on my limited knowledge of the codebase. Feel free to update directly the PR or close it if this was not the right fix/thing to do :)

I managed to replicate my issue directly in the example directory with my login and sponsors, without changing the sponsor.config.ts file. Here's the result when I run pnpm run build:dev in this directory with my GH login:

Scope: all 2 workspace projects
Done in 745ms

> @ build:dev /Users/ju/sponsorkit/example
> esno ../src/cli.ts

                                                                                                                                         2:54:02 PM
SponsorKit v0.16.1

✔ Loaded from cache ./sponsorkit/.cache.json                                                                                            2:54:02 PM
ℹ Generating with 3 renders...                                                                                                          2:54:02 PM
ℹ [sponsors] Composing SVG...                                                                                                           2:54:02 PM
ℹ [sponsors-wide] Composing SVG...                                                                                                      2:54:02 PM
✔ [sponsors-circles] Wrote to ./sponsorkit/sponsors-circles.json                                                                        2:54:02 PM
ℹ [sponsors-circles] Composing SVG...                                                                                                   2:54:02 PM
node:internal/fs/promises:1049
    validateStringAfterArrayBufferView(data, 'data');
    ^

TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received undefined
    at Object.writeFile (node:internal/fs/promises:1049:5)
    at <anonymous> (/Users/ju/sponsorkit/src/run.ts:324:19)
    at Array.map (<anonymous>)
    at applyRenderer (/Users/ju/sponsorkit/src/run.ts:293:29)
    at <anonymous> (/Users/ju/sponsorkit/src/run.ts:230:7)
    at async Promise.all (index 2)
    at run (/Users/ju/sponsorkit/src/run.ts:224:5)
    at Object.handler (/Users/ju/sponsorkit/src/cli.ts:55:5) {
  code: 'ERR_INVALID_ARG_TYPE'
}

Node.js v20.12.2
 ELIFECYCLE  Command failed with exit code 1.

With the modification of this PR, the images are well generated. So it might not be as I thought in the issue that the formats option is mandatory, but rather than by default there's json in it, and it crashes in the middle of the algorithm.

After having added a lot of logs, I managed to find out that data is undefined because the format is json at this moment. Since it's not svg, png, or webp, data is never filled out in the algorithm. So whenever the path was /Users/ju/sponsorkit/example/sponsorkit/sponsors-circles.json, the data was undefined.

Hopefully, it doesn't break any other use cases folks might have 😬

Linked Issues

Closes #98

Additional context

I've also tested to change sponsor.config.ts to use the one in my project: https://raw.githubusercontent.com/julien-deramond/static/refs/heads/main/sponsorkit.config.ts, and it worked too.