refactor: drop cosmiconfig

[satya164]

Summary

cosmiconfig is no longer maintained. Apart from that, we can't support ESM configuration properly because cosmiconfig only supports loading it asynchronously - but we need to be able to load it synchronously in babel config.

I also took a look at lilconfig, but it also has the same limitation.

Node 20.19.0 onwards supports synchronous require of ESM, so this limitation is not a technical limitation. So I decided to implement config loading myself since we don't need any advanced features of these config loaders such as traversing up until they find the config.

Test plan

Tested in a sample project with both bob build and in the example app with metro.

[Copilot]

Pull Request Overview

This PR refactors configuration loading by dropping the deprecated and limited cosmiconfig in favor of a custom synchronous loader. Key changes include:

• Removal of cosmiconfig and lilconfig dependencies.
• Implementation of a custom loadConfig function for synchronous config loading.
• Updates to configuration loading in babel-config, init, and build scripts.

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

File	Description
packages/react-native-builder-bob/src/utils/loadConfig.ts	Implements a custom synchronous configuration loader, including special handling of package.json.
packages/react-native-builder-bob/src/init.ts	Updates config loading to use the new loadConfig with an explicit root parameter.
packages/react-native-builder-bob/src/build.ts	Uses the new loadConfig synchronously instead of cosmiconfig.
packages/react-native-builder-bob/babel-config.js	Replaces cosmiconfigSync with the new loadConfig and updates error handling accordingly.

Files not reviewed (1)

• packages/react-native-builder-bob/package.json: Language not supported

Comments suppressed due to low confidence (2)

packages/react-native-builder-bob/src/utils/loadConfig.ts:65

• [nitpick] For errors other than MODULE_NOT_FOUND, the code rethrows the exception; consider adding an inline comment to clarify why non-module-not-found errors are rethrown to aid future maintainers.

throw e;

packages/react-native-builder-bob/babel-config.js:20

• The thrown error message ('Couldn't find a valid configuration.') might be too generic; consider specifying that no configuration file was found in the expected search places to improve clarity.

if (result == null) {