Adding a new workspace folder breaks things

### How are you using the lua-language-server?

NeoVim

### Which OS are you using?

Windows

### What is the issue affecting?

Completion, Diagnostics/Syntax Checking, Hover, Libraries

### Expected Behaviour

Addding new workspace folders should not break anything.

### Actual Behaviour

Right now, adding a new workspace folder breaks two things, diagnostics and require statements:

- You can fix the diagnostic errors by hooking to the `workspace/diagnostic/refresh` handler to manually refresh it, but even then this is very unreliable and prone to not working:
https://github.com/neovim/nvim-lspconfig/issues/2366

- `require` statements that refers to modules in the new workspace folder also does not resolve correctly (hovering over the module string will display the byte length, instead of the resolved path). This means that completions from the required module will also be missing. So far I can't find any way to fix this without restarting neovim entirely.

Other LSP servers doesn't have this problem. Adding a new workspace folder should _just_ work without any additional steps.

### Reproduction steps

1. Initialize the LSP server with a root directory
2. Add a new workspace folder using `workspace/didChangeWorkspaceFolders`
3. Opening a file from that workspace folder results in diagnostic errors and modules not being resolved correctly

### Additional Notes

_No response_

### Log File

_No response_

Start by reproducing the reported sequence: initialize with a root directory, send workspace/didChangeWorkspaceFolders, and open a file in the added folder. Investigate how workspace/diagnostic/refresh and require-module resolution behave afterward. Done means diagnostics, hover paths, and completions work in the new workspace without restarting Neovim or relying on manual refreshes.

Written by the indexing model from the issue text.