fix: rollback node-fetch to v2

[Nonolanlan1007]

This fixes a bug introduced in v2.6.1 that caused errors for users who did not use ESM:

Node.js v20.11.1
/node_modules/@discordanalytics/core/dist/index.js:41
const node_fetch_1 = __importStar(require("node-fetch"));
                                  ^

Error [ERR_REQUIRE_ESM]: require() of ES Module /node_modules/@discordanalytics/core/node_modules/node-fetch/src/index.js from /node_modules/@discordanalytics/core/dist/index.js not supported.
Instead change the require of /node_modules/@discordanalytics/core/node_modules/node-fetch/src/index.js in /node_modules/@discordanalytics/core/dist/index.js to a dynamic import() which is available in all CommonJS modules.
    at Object.<anonymous> (/node_modules/@discordanalytics/core/dist/index.js:41:35) {
  code: 'ERR_REQUIRE_ESM'
}

[ValDesign22]

@types/node-fetch and node-fetch can be imported only in the core package, no need for them to be imported in the sub-packages

[ValDesign22]

why not use the native fetch function from node instead of node-fetch?

[Nonolanlan1007]

https://linear.app/discordanalytics/issue/DA-110/remove-node-fetch-dependency

[github-actions]

🎉 This PR is included in version 2.6.2 🎉

The release is available on GitHub release

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