Improve test coverage and add troubleshooting docs

[Dark-Brain07]

Description

Hey, I was going through the connect package and noticed test coverage was pretty limited - just 2 test files for the whole thing. Also there wasn't really any troubleshooting guide for developers running into issues.

So I added tests for the utility functions that weren't covered (things like network conversion, Clarity value handling, Taproot address detection), improved the docs with better JSDoc comments, and wrote up a troubleshooting section in the README covering the common problems I've seen developers run into.

I also threw in a few extra error codes that seemed useful and a helper function to make error handling cleaner.

Changes:

• New test files for utils.ts, errors.ts, storage.ts, auth.ts
• Better JSDoc documentation in utils.ts
• README now has troubleshooting section with common issues
• Added error codes like NetworkError, TimeoutError, ProviderNotFound
• New isJsonRpcError() helper for cleaner error handling

Type of Change

• New feature
• Bug fix
• API reference/documentation update
• Other

Does this introduce a breaking change?

Nope, everything is additive. No breaking changes.

Are documentation updates required?

• Already included - README troubleshooting section and JSDoc improvements

Testing information

1. Run npm test in packages/connect to verify
2. Not a bug fix
3. Touches utils.ts, errors.ts, storage.ts, auth.ts
4. No other projects affected
5. All new tests should pass, no changes to existing behavior

Checklist

• Code is commented where needed
• Unit test coverage for new or modified code paths
• Changelog is updated
• Tag @jannik-stacks for review