[ty] Implement workspace/didChangeConfiguration

[pharmac1st]

Summary

Implements astral-sh/ty#953

Adds a notification handler for workspace/didConfigurationChange. Re initializes workspaces when this is received with the newly pulled settings.

Workspaces are just reinitialized with a new settings passed from the client.

Copied code from #20545, so credit to @Guillaume-Fgt for that.

Test Plan

I've added a unit test in configuration making sure this runs successfully. I am unsure if this is sufficient so please let me know how I can improve the testing implemented in this PR.

[MichaReiser]

Cleaning all workspaces just because e.g. the selected interpreter is a bit rough :)

Are there any settings that change the known workspaces? Is there a way we could only update the settings or is this much more complicated?

[pharmac1st]

Yea, initially I had considered some kind of diff checking to see what specific workspace settings had changed, but it seemed quite complicated between the pulled ClientOptions and the existing WorkspaceSettings in terms of implementation. If we could find a good solution for that we could:

A. Only update workspaces that we knew had changed
B. Only update the specific settings that had changed

Potentially this is done through manually comparing each setting on the two structs (and maybe returning or modifying the existing WorkspaceSettings)? Please let me know if you have any ideas 😃 .

[pharmac1st]

We could also just replace Arc<WorkspaceSettings> with the pulled settings as well, potentially we don't need to reregister and reinitialize unless the configuration file has changed? (This is the only thing I can see relying on settings in initialize_workspace_folder - https://github.com/pharmac1st/ruff/blob/a9ffadb41636a472c5a8a52aedca350ad64a8ac1/crates/ty_server/src/session.rs#L592).

We could also move handling updating global settings in update_workspace_folders, and not rely at all on initialize_workspace_folders.

[MichaReiser]

I'd have to take a closer look, but just overriding the WorkspaceSettings seems fine; we don't need to diff them. But we also need to re-resolve the settings passed to the ProjectDatabase. It's okay if we replace the options if they don't compare equal, but that we should avoid is creating a new ProjectDatabase because that clears all caches

[pharmac1st]

Updated - I saw there was reload() which sort of did want we want, I split this function out into a more specific one that updates the settings.

I've also assumed that we want to update the global settings as well, and that should be set from the last workspace received (similar to how it's done in initialize_workspace_folders).