[Bug]: http-client-java, support Client / SubClient in different package

### Describe the bug

https://github.com/allenjzhang/typespec-e2e-demo/blob/cd13f41abb54bb86f80eeabfdefb1e48e3e59321/todoApp/spec/main.tsp

There is nested namespace that contains operations.
It would result in Client / SubClient in a different Java package.

Currently the Client in Java is initialized via package private constructor, hence the Client and SubClient be in same package.

### Reproduction

https://github.com/allenjzhang/typespec-e2e-demo/blob/cd13f41abb54bb86f80eeabfdefb1e48e3e59321/todoApp/spec/main.tsp

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.