Closes#1952
API 1.3 adds a diagnostics provider for unsaved documents: the host sends versioned text for the declared languages after a 300 ms debounce, cancels superseded calls, drops late or stale answers under the editor-provider budget, and clears results with the document, project or plugin. Ranges are UTF-16. Actor panics are contained, queued work is rejected after a host panic, and diagnostics arriving after plugin cleanup are discarded. Verified on macOS with the diagnostics fixture.
Co-authored-by: arnaud-ritti <[email protected]>
