Make client requests type safe, unmarshal

[jakebailey]

This PR makes server-to-client requests typesafe using the same info structs used everywhere else.

As part of this, I figured out that our client requests have not been decoding properly at all; they have just been going through the default Go json decoding. This has not bit us because we either ignore the result, or we wanted []any (for settings), so it just so happened to work. This PR also fixes that problem, so we are now actually decoding the responses.

[Copilot]

Pull Request Overview

This PR introduces type-safe server-to-client requests by leveraging RequestInfo structs with generic type parameters. The key improvement is that client request responses are now properly unmarshaled using type-aware decoding instead of relying on Go's default JSON unmarshaling.

Key Changes:

• Replaced sendRequest with generic sendClientRequest function that uses RequestInfo[Req, Resp] for type safety
• Changed ResponseMessage.Result field from any to jsontext.Value to defer deserialization
• Added unmarshalResult function (and generator code) to properly unmarshal response results based on the request method

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/lsp/server.go	Migrated all client request calls from sendRequest to type-safe sendClientRequest, properly typed response handling
internal/lsp/lsproto/lsp.go	Added UnmarshalResult, NewRequestMessage, and NewNotificationMessage methods to support type-safe request handling
internal/lsp/lsproto/lsp_generated.go	Generated unmarshalResult function with method-specific unmarshaling logic for all LSP request types
internal/lsp/lsproto/jsonrpc.go	Changed ResponseMessage.Result to jsontext.Value for deferred deserialization; removed old helper functions
internal/lsp/lsproto/_generate/generate.mts	Added generator logic for unmarshalResult function to handle response type unmarshaling
internal/fourslash/fourslash.go	Updated test helpers to use new NewRequestMessage and NewNotificationMessage methods from info structs